I quoted this from a rc car site. Im sure alot of the same principles apply to cars... Most sportbikes also have inverted shocks...
1) Upside down shocks lowers the truck's center of gravity. It's not so tippy in the corners.
Okay so this is inverted.
so the above doesn't make sense. Obviously inverted (or up side down) the heavy part is on the top which in a small way throw off the center of gravity (less stable in cornering)
2) Reduces shock oil leakage. When your truck sits, unless your seals and shaft are brand new, a tiny bit of fluid leaks out of the o-ring seal. Over time, this adds up. With the shocks upside down, the oil is now contained by the better seal, at the cap of the shock.
Again, looking at the pic above, the leak would like down the shaft at the bottom...which doesn't reduces shock oil leakage to me.
3) The air bubble is now moved to the other end of the shock piston's stroke. Let's face it, who doesn't have a tiny bit of air in their shock? With your shock right side up, the piston enters the air bubble when the shock is at maximum compression, such as when you come off of a big jump. This is exactly when you DON'T want this to happen. When the piston enters the air bubble, all resistance to movement is gone and the truck bottoms out. Upside down shocks eliminate this problem. The only time the piston enters the bubble is when the shocks are at maxximum extension (such as when your truck is in the air). I think it's beneficial to have a little bubble at this time since your shocks more easily reach maximum extension.
With inverted shock, the air column sits on the top which is when the shock is at max compression...opposite of what stated above??
4) It draws a lot of attention. When I first bashed with other people with my shocks upside down, everyone noticed. Some people thought they were being funny by telling me I accidently mounted my shocks upside down. Well, the smile was wiped off of their faces when they saw my truck's increased performance.
So far, there are two negatives I can think of:
1) Upside down shocks increase the truck's unsprung weight. In theory, the lower unsprung weight relative to the sprung weight, the more responsive the suspension will be. However, given the already high unsprung weight of an e-maxx, I don't notice any difference.
2) The shock's body is more apt to be hit by debris. So far, though, I haven't had a problem with damage since the upper a-arm shields it pretty well.