SCOM has two alert types. Monitors and Rules.
Both need to be handled differently when resolving. Normally Monitor alerts will self close when the alert has been resolved, but in some cases we have users who will inadvertently close a monitor alert.
It can also be difficult to have users fully understand the difference between a rule and a monitor, and act appropriately.
If the monitor alert is closed, and the underlying issue not resolved (eg low disk space), then you will not get further alerts unless the health state changes back to healthy and then unhealthy again.
Ideally it's easier to tell users just to "close" alerts, and not to have "reset health".
This posting on the Technet Wiki was one solution I'm implementing to make it easier for users.