Group Policy foreground refresh is a little bit different in that it is only triggered by specific events. These events include boot or shutdown of the computer, as well as user logons or logoffs. Foreground refresh sequences are the only times that something like a logon or logoff script would be able to be processed.
Knowing the differences between refresh cycle types is necessary because some of the switches that can be used with GPUpdate initiate different tiers of the refresh cycle. Here is a list of those switches.
