I always keep 1-2 bags to be "regular" bags, or in the case of a bot who only herbs or only mines, you can get 2-3 specialized bags. Always keep 1 regular bag because there are always some things that can't go in the specialist bag (gems) etc. GB doesn't notice which type of bag u have and if there is an empty slot, but not of the right type, the bot will attempt to gather nodes even if it cant loot, eventually it will blacklist the node and move on. I found its much more reliable to use the mailing function, cause it mails every time it does a repair run. Bags never get full that way.