XP?

So I know you need XP to evolve from baby to adult, but what is the point of XP after that? Like I used a booster and it's going to last well after my pet is evolved, I don't know if it helps to keep gaining with them till it runs out or just call it a loss of the booster and move on to the next.

I will likely add Levels to pets eventually and we may have another evolution someday.

ok, that'll be neat, so yes keep stacking up XP on all of them for future purposes. Got it. ;) TY