Consider very carefully if you want to use this, it is very strict. Therefore non standard browsing, with unusual session handling (such as games consoles, multimedia devices) it is likely to log that person out. Two browsers, it will log out.
If you are offering certain premium services which are dependent on one session, this can be useful.
Those with Admin/Garden.Settings.Manage privileges are immune.
Tested on 2.0.18, 2.1b2