Why would I level up Assist Units?
In Memoria freese, You have assist units tied to your main unit. these units apply a stat bonus to the unit(s) or debuff the enemies in the form of a skill. However, these units also have their own set of regular stats, like HP. They aren't in the battle though. So why would I level them up or release their status board?
Their stats don't seem to increase the Main Unit stats at all, unless I am misreading something.
Their stats are added to the character that you have them set to assist.
By this token, you should consider to use high STR assist characters with your characters that use STR, etc.
Since leveling up a character increases its stats, it is beneficial to level up your assist characters.
Here is an example:
The strength starts at 51. Hestia's 23 strength is added for a result of 74 strength.