SD is not very important at all in most cases. If you are shooting beyond 500 yards with a 1/2 MOA firearm, then it becomes something to consider. The other case it might be important is if it is seriously higher than normal. That might also indicate a loading error.
The commercial ammo I have checked (not many cases) tended to have about a 35 FPS standard deviation. The worst was some of the special high energy stuff, which was about 65 FPS.
My rifle handloads tend to be around 25 FPS or so. Handgun loads tend to be in the single digits or low double digits. I got on a kick once, and loaded some 223 that was in the single digits. I couldn't see any difference between that and the regular stuff.
