The Fediverse has a much smaller user base than other platforms, so if you're primarily looking for a wide audience then it might not be for you.
Not all Fediverse projects are at the same stage of development and some important functions one projects has, the other might still be missing.
Fediverse projects and instances are run by volunteers with not a lot of money behind them. Worst case: A project might no longer be maintained or an instance might close.
There are some instances that allow hate-speech, fake news or worse. Make sure you don't end up on one of them.