Hey, Yasinoz. When it's under a bobber, it doesn't really matter too much. Sometimes, it's nice to have a lighter jig because it falls slower. Sometimes, that can entice a strike. The size of the jig can make a difference at times as well, and fish can kinda change what they want through the day, so it's good to have different weights, sizes, and colors. That's not to say go out and buy a bunch of jigs. You can get away with anything, especially with bluegill. I'd say go as light as you can, unless that's not getting you deep enough as fast as you want it. Imo their really is no set rule. Each water will fish differently, just avoid the snags. I personally fish 1/32 and 1/16 the most. Sometimes, I'm looking for even smaller if they're small fish or if I want a slower presentation. I only go heavier if I'm trying to get deeper into the water column. Good luck!