What are manda best use for?

Just new to this game.

So the cash coin, manda. What should i use them for?
Recruiting new characters?
Refilling?
Or should i wait for events which have 3* rate up? (is there such event?)
Or something else?

Please advise

For the latest event, papillon, was it a 300% rate up for scroll too? Or manda use only?