As it is with blood magic, aura's take a snapshot of their support gems when cast. You can use this to help with certain gems types.
Example: Clarity + reduced mana. Cast Clarity, then move reduced mana to a actively used skill.
It could even be useable with summoner builds, although very annoying to have to switch everytime you re-cast all your zombies or spectre's, but it would cut the minion dmg/speed/health/+weapon dmg gems you need down.
This will obviously also free up the gem slots allowing you to either lvl low gems or just use other gems.
Shelk