Playing each class requires 2x char slots (for active char and mule to carry extra not used gear that may be used in the future), an active stash tab for each char (to handle Armory build variations and experimental gear), generalized Ring and Armor and Weapon stash tabs (to support common weaps, rings, LOD and experimental builds), and a generalized Gem stash tab (for Gems across multiple builds, Keywarden keys, R-Gifts, leveling Augments, misc stuffz).
This doesn’t leave a lot of leftover stash space and char slots … especially when new sets are introduced and the number of active builds/playstyles want to be played. Juggling space for active Armory builds becomes more and more difficult, especially when more combos of LOD builds are available across classes.
Think the problem is related to different class main stats … which forces keeping multiple copies of same/simuliar items items for builds to take up space. Hopefully, D4 won’t have this issue.