Even if you pay for the product, using SaaS products VS hosting your own software, still puts you under someone else's control. The feature you really needed from them, might be decided that it should be removed, because only 1% of the total users actually used it, and you'll have no recourse.

This has happened time and time again with most SaaS, and will continue to do so, unless some new model arrives where each user can run their own version.