I noticed recently in some screen shots posted by MD44 and Animal that their grass seemed to look a lot better than mine, so I investigated...
In the system settings in DCS there is a slider for Clutter/Grass. It can be set from 0 to 1500. I noticed mine was set to 0. When we're flying fixed wing aircraft that's probably good enough, since we spend so little time near enough to the ground to admire the grass, and when we are on the ground we're normally on concrete. But in helicopters we spend a lot of time right at ground level, and we take off and land out in the fields.
So...I moved mine up to 1500, the max, and you can see in the before and after screenshots below, what a difference it made. And as far as I can tell it didn't have much of an impact on frame rates.
The only real downside I can see is there are a lot more places for snakes to hide.