Monster: Worth Keeping?

I've got a sh'load of 3* and 4* mobs... do Ineed to keep them? Aside from not having any defenses towards attackers do they serve a purpose?

They serve a few purposes.

1. They detour attackers.

2. Some can be recruited either not or in future events for usable units.

3. 4*-6* monsters are worth more than 4*-6* units when trading in for the future recycling event.

Unless you do not care about attackers stealing your artifact and/or
Lunas, you can sell the monsters or use the monsters as
feeders. If you are going to keep your monster, you need to level
Them up, or it is pointless keeping monsters in your roster.
I wouldn't say monsters are "worthless." They do serve a purpose
in the game. It just depends on the player if they want to keep them.

if you have a minotaur KEEP IT

Any reason to keep chimeras. ? Besides Minotaur what other 3s should we keep

(bees, poisonous flowers)(possible to recruit with minotaur)

harpy(recruitable)

salamander,treant,Troll (good def once lvl)

oh yeah i forgot kappa is also going to be recruitable