Think of it like pushing a wheelbarrow. The angle from the axle to the handle is like caster. Pick up a wheelbarrow and stand it vertically on the tire with the handles straight in the air. Imagine pushing it and trying to turn it. Now, imagine pushing and turning it normally and notice how much easier and stable it would be. When you turn a wheelbarrow notice there is no steering, the front wheel leans! That is how motorcycles turn as well, and to a less exaggerated extent that is how your car turns too.
Not all camber arms are adjustable....
Not all camber arms are adjustable. These EF upper arms from Cusco forego adjustability in favor of upgrading to stronger uniball joints rather than ball joints. These arms also add negative camber.
Caster is great for high-speed stability. That is why all cars have some dialed in. Without it, the car would be twitchy and hard to control. That explains why autobahn burners have more caster than your typical Japanese car. It doesn't greatly impact tire wear on its own, but it can induce a pull in the suspension if it is drastically different from side to side. Excessive caster will cause slow and lethargic steering and combined with toe-in, it is downright deadly for tires.
Camber gets somewhat of a bad rap within the automotive industry. The typical premature wear pattern people notice on a lowered car is due to excessive inner tire wear. People naturally associate the leaning of the wheel with this inner wear. Thus, they determine the fix for the wear is to install a camber kit which will allow adjustment of the camber. If tire wear is your concern, know that camber alone is not to blame. The reality is that a bad toe setting will wear tires much faster than camber will.
Actually, camber can be a very good thing. To some extent, some negative camber will actually benefit the car. When a double-wishbone suspended car such as the '88-'00 Civics, '90-'01 Integras, Accords or TSXs, the camber angle always increases in a negative direction whenever the suspension moves up. It's what makes the car handle better in turns than the strut cars, which have negative camber but not nearly as much, generally speaking. It is a natural affect of cycling a double-wishbone suspension.
This upper control arm has...
This upper control arm has an adjustable ball joint mount. Care should be taken to opt for an arm with a high quality ball joint, such as this Ingalls unit.
As the car is turning hard, the outside suspension becomes loaded and the tire tends to roll under the wheel rim. With a zero camber setting, the tire would be aggressively pulled under and the car would actually be riding on the outside of the tire with a reduced contact patch. As a double-wishbone suspension is loaded, the camber angle becomes more negative tilting into the turn and effectively pulling the tire back under the wheel through the turn. The end result: With negative camber the contact patch will be larger through turns.
Imagine that when such a car is lowered, the suspension's neutral stance will actually be the result of moving the wheels up as though they were "preloaded." The suspension "thinks" it is constantly cornering, even when it is going in a straight line. Camber is negative and toe is in. On-center feel generally deteriorates, as do the tires on the inside edges.
At this point, you may be wondering what is doing the damage to the tires the toe or the camber? To answer the question we must forget conventional wisdom and simply look at some tires.
Look where the inside and outside of the tire are. The red circles [above] are there to help you identify the wear-indicators inside the tire grooves. When the tires wear down to these wear-bars, you know it is time to replace the tires. These tires are almost there. You can see how the tire is worn more toward the inside. This is camber wear. This car was lowered moderately with a good alignment. The person who drove on this tire has not maximized tire wear, but clearly hasn't suffered greatly either. No camber kit was installed to fix the camber.