LogFAQs > #877042688

Well, one of the things about it is that your character tends to level up faster than your persona levels up (unless you have certain abilities that increase persona experience).

So in the long run you end up with a character say level 20 and a persona that's dragging back at level 12.

Yes you can keep them, but it might be a stronger option to fuse stronger personas.

Once you have money, you can always re-summon any persona you've previously owned from the Compendium. That's what that is for. So you can re summon things, fuse things, make new personas, then fuse those, and then when you need personas to fuse you resummon old ones. It can use a lot of money but you can end up with a lot of strong Personas.