Best practice as taught on any training courses is to always groom as the last step in the process. Not only does it even out the appearance but standing the pile up will help it dry quicker. If I had a carpet that showed really distinct zig-zag marks all over it after cleaning I wouldn't be happy with the finish!
I don't groom every single carpet after cleaning but always on wool. It can actually set the pile the way you've left it on some carpets, believe it or not. I don't always bother on polyprops, rarely on rentals and never on any loop pile carpets that don't show wand marks.. .what's the point!