In BG3, Hide and Potions are bonus actions, so obviously quicken is not needed for those. Dash will basically never be useful for spellcasters in BG3 because of the smaller maps. Oh and I completely forgot to mention Dodge. Dodge (+ mirror image & shield) is pretty powerful in tabletop against attack rolls and Dex ST effects; get in the middle of combat, quicken a powerful spell and use your action to Dodge, then shield any hits that get through! ...but of course Dodge doesn't exist in BG3.
This.
Another really strong Quicken spell combo is to use Greater Invisibility (stay invisible after attacking/casting), and then just cast spells via Quicken and take the Hide action every turn.
People who need to use sight automatically fail their perception checks unless they can sense you another way (tracks, noise, etc). On failure, they they don't even know where you are and cannot target you at all. For those who manage to pass the perception check, if they don't have the ability to see invisibility, they still attack at a disadvantage + can't target you with many spells. If you're a Clockwork Soul sorcerer, you can get the non-detection spell and make yourself immune to trueseeing / see invisibility just as an added layer of defense on top of that.
Very expensive to pull off, but very powerful.
Right now, with Hide being a bonus action, this powerful combo is available to all spellcasters once they get greater invisibility... without the need to expend sorcery points to cast in the same turn. This is one of another design choices that haven't accounted for scaling.
