Probably it's more frequent that a connected user even idle for 5 mins, start again to browse a document, this is just an assumption.
Unfortunately there's no email advice when your server reach the max session limit, but if you need it, you can use the "Performance.log" generated from QVS for count Doc Sessions and generate an email.
JSiddoway wrote:How is that different than simply removing their license and having User 1 re-acquire a license when they become active again?
When a session is closed, the user's selection state is lost, which may irritate the user if they return to the document. The two options allow you provide flexibility to users in slow times and effective license utilization when demand is high. A typical setup might be:
Maximum Inactive Session Time: 1800 (30 minutes)
Possible Session Timeout: 300 (5 minutes)
So when there is no demand exceeding your license, users can idle for up to 30 minutes. But during busy periods when demand exceeds your license, user may get timed out somewhere between 5 and 30 minutes.