I've recently had an inquiry about compressible washers. If you've changed your own oil, you probably know what I'm referring to: it's the washer on the shank of the drain plug of your car's oil pan. When you unscrew the drain plug, it usually remains stuck to the oil pan, and subsequently gets pried off with the edge of the open-end wrench you just used to remove the plug itself.
The particular discussion: is the washer necessary?
Yeah, I know it's a pain, but I use new washers on the drain plugs of my own vehicles. Typically, I buy ten washers at a time from the dealer's parts department. They're cheap enough, even at $1.50 a piece, which is about what they retail for. If you buy in bulk, ask the parts guy if he wouldn't mind selling them to you at the wholesale price. Usually it's about 20% off.
My personal experience with changing oil, in conjunction with what I've learned in my formal engineering education, is that it is wise to use the washers. Both my Mercedes and my Lexus use them, and there's a reason the manufacturer designed the washers into the system. As your engine heats up, metal expands. When it cools, metal contracts. When this occurs between two different parts, especially of two different materials or masses (thermal capacity and flow rate is related to mass and density), small relative motion can and does occur between the two parts. This frequently causes fasteners to loosen, even if they've been torqued to specification. Add in vibration, which is endemic to a reciprocating piston engine, and this relative motion is exacerbated. That's why the washers are there, and coated with a material that not only crushes and locks into macrosurface irregularities, but also dampens the effect of vibration and helps the fastener resist this tendency to move relative to the oil pan into which it's threaded.
I don't want to disparage anyone, but I have frequently encountered the attitude of "hell, I don't see a need for this part, so why bother putting a new one back on?" Usually, it's laziness that prompts such a reaction; it's easier to think of a reason not to do something than it is to expend the money, energy, and time to perform a task that has no clear reason to be done. Many people approach life that way, too.
From a perspective of risk assessment, the benefit of the washer far exceeds the cost. Lose the drain plug on a running engine, and that engine will be completely ruined in seconds. Then you're faced with the choice of installing a junkyard engine that's had questionable maintenance and has probably been salvaged from a crashed vehicle, or purchasing a remanufactured engine that was assembled from a bunch of aftermarket parts tossed on a table, or rebuilding your own damaged engine, if that's even possible. On a Toyota four-cylinder, the total cost of the engine and installation might run $2000 to $3000. On a Lexus or Mercedes, the cost could easily approach $5000 to $8000. And on a Ferrari 550 Maranello, a replacement engine can run from $15,000 salvaged to over $30,000 new. And remember, with the exception of a new OEM unit, the replacement engine is probably not going to be as well-maintained as the one you just burned up, because if you're reading this, and you change your own oil, you probably bought a vehicle in good condition to begin with, and you're diligent about taking care of it.
As a sidenote, an engine doesn't even have to lose its oil to be severely damaged from oil starvation. The C5 Corvette and the Generation I, II, and III Dodge Vipers could generate enough cornering acceleration to slosh the oil from the bottom of the oil pan and hold it up against the sides of the oil pan and lower engine block. This uncovered the oil pick-up, which immediately starved, and in a matter of seconds, the engine became unlubricated. The C5 engineers figured this out in testing, and designed and implemented a special cast aluminum oil pan that had internal baffles to keep the oil pick-up immersed in oil, even in hard cornering. The Viper's problem manifested itself when owners began racing their cars on tracks with long, fast, sweeping turns, and when the oil pick-up starved, if I recall correctly from my conversation with Chuck Tator, the number three bearing journal would seize. Generation IV Vipers, beginning with the 2008 model year introduced in 2007, use a swinging arm oil pickup that articulates to the right or left of the oil pan during hard cornering. This follows the oil and keeps the pick-up immersed. It's important to note that these problems only occurred during extreme performance maneuvers, and not in the normal kind of fun driving that these cars can so capably and wonderfully deliver.
Also as a sidenote, this is why certain performance cars use what's called a 'dry-sump' oil system. In a dry-sump system, there isn't a conventional oil pan hanging under the engine, filled with a gallon or two of sloshing oil; the oil is stored in a reservoir near the side of the engine, and upon start-up, there are multiple feed and scavenge pumps that force pressurized oil into the oil galleries of the engine and spray the oil into critical areas requiring lubrication. There are several advantages to this: without that deep metal oil pan under it, the entire engine can be mounted lower in the car, much closer to the ground. This results in a lower center of mass, which directly translates into better handling. Dry-sump lubrication is also immune to extreme cornering forces; the oil will be circulated where it needs to go, regardless of the forces acting on the car. It's also easier to remove heat from the oil, which is critical in extreme performance applications. Detriments? The system is more complex than a conventional oil system, which means it's more expensive to design and manufacture, and it's typically only used on high-end performance cars.
A word about filters: I haven't seen any SAE studies on types or brands, so I wouldn't endorse one particular brand over another. Personally, I'd stay away from the bottom-tier cheapest filters, but if you stay with OEM or a well-known aftermarket brand, you should be fine. There was an issue with some defective imported Italian oil filters that blew apart on some Ferrari engines several years ago, but from what I've learned, this was because the metal wall thickness of a particular batch of filters was too thin for the oil pressure that those engines were generating.
The most important factor is simply to get a new filter on at every oil change. And I'd recommend using a new washer, too.