ALT + F4 is a very simple way to close'em totally but it is ok to simply slide them down like on W8. When pulled down, they don't use any resources
I think that the ideal is to close one by one. Maybe this tweak to speed up applications you interested. Code: Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Serialize] "StartupDelayInMSec"=dword:00000000
It may be better to remove them from the start screen, so you won't hit them accidentally when trying to start a desktop application. If it's not running, you don't need to close it.