I see mostly two context(s) for multi-verses....
The main-verse is stagnant and boring (or can't be tinkered with) so it's time to spice things up with an alternate universe where better stuff can happen.
It fixes a dead end or plot hole.
We've taken our world/story to the end and need a reset button.
We killed someone that the FANS really miss so we're bringing them back.
I can't think of anyone doing the multiverse thing that wasn't trying to fix something.
I think the best has been when there was an alternate 'future' that we were allowed to live in for a short while.
It takes a super talent to pull it off.
- to make a world that is 'better than the first'
- spend enough time to make it feel real
- have some repercussions that affect the whole story
- not SO GOOD that we don't ever want to leave or would rather follow that world than the main universe story.
Old school, I think the Matrix and the early Terminator movies did it well.