Yes, a side account can be searched in your free time re-rolling in your spare time [I once re-rolled 3 SSR Himes and 2 SSR Eidolons in a 6k Jewel re-roll ), with luck you might end with a better account than your main and switching, worse case scenario you have a strong spare account that you can use to summon Disaster Raids during an Advent Battle where you can't afford to spend AP or even help you in Raid Events when no one summons said Raids or Aid you while maintaining your MVP on your main account, it is really helpful