As a gnome, I'm assuming you want to be enlarged to fight another gnome or svirfnebli, perhaps enlarged against other mid-size foes as well,
And then reduce yourself against giants, so you are too small to bash?

Any other advice regarding how to use reduce and enlarge in general? Not feeling like I have the strategy down as to when it's important or what defensive/offensive abilities are noticeably impacted. My guess is there's more to it than meets the eye.