How many Restart Computer after each new Program Install?

I only restart when prompted, but not always. When I have a lot of things to install, sometimes I leave it at the end.
Regarding Winxp updates, I ALWAYS restart, bacause there was an issue when you install 2 updates and the first has newer version of a file than the second, then, the newer version is overwritten by the old one. It's kinda tricky:hmm:

 

I restart only when needed. Always for drivers, seldom for apps/games. I dismiss the restart needed prompt, I run the app/game and if it starts then there's no need to restart. If I get an error message, I it will clear after restart. Or maybe not. Whatever the case, I restart manually. But if I'm able to use the said app/game I don't bother restarting until I encounter the first app that really needs a reboot.