We feel strongly about not disrupting people and organisations' workflows with too many (or rigid) processes. It can happen that you need to quickly add user accounts, even if you reached your plan's maximum, and having to take care of the upgrade would be an unwelcome annoyance. This is why we offer a “tolerance” ratio: you can add up to 10% (but not more than 50 users) additional users beyond your plan's limit before being required to do the actual upgrade. You'll be reminded that you are in a “red zone” but are free to plan the upgrade at your convenience.