And while important in all distance shooting, drop and wind drift become critical in varmint shooting. A half inch wind drift error might make no difference at all on a deer, but on something where the vitial area is half the size of a soda can, it can be the difference between a clean kill and a clean miss.
A 2MOA rifle/ammo combination is fine for deer and bigger game, barely tolerable for big woodchucks (at shorter ranges) and totally unsuited for smaller animals or really long shots. Even though 2MOA means all shots will be within 1" of point of aim, for some applications its just not good enough. And that's without the complication of wind and drop.
Each caliber (cartridge and bullet configuration) will have its own specs on drift per mph of wind, and to be accurate, one needs to not only know what that is, but be able to accurately judge the wind speed, and direction relative to the bullet flight path.
You can learn the principles out of a book, but you can only learn reality from field experience.
All else being equal (and it almost never is) bigger bullets tend to work better.