Here in SD the trees are few and far between. CRP provides great cover for deer as well as pheasants, grouse, and any other critter for that matter.
The original purpose for CRP(at least here) was to stop land erosion and the land you want to enroll still has to have some amount of land erosion for it to be allowed into the program, but about 95% of all land here will qualify.
Not really sure of any downsides to it. Unless the land would be good farm ground, then you can no longer farm it but that is not usually the case. maybe another downside is that CRP provides cover for, fox,coyote, skunksa nd a host of other varmints.
Hunting isn't a matter of Life or Death
Its MUCH more important than that!