Originally Posted by Unregistered

Any tips on what to do with duplicate 4 star or higher units? I'm thinking just keep them? I don't know if it's worth sacrificing all their stats for an extra equipment slot and a chance to get a 1% increase on skill.

No real point in keeping them. As the game goes on you will be swimming in them. Use them for the extra gear slot/skill ups. Not to mention all the resources you would waste on leveling a second copy when those resources could be better spent on leveling your initial 4* and higher units.