Installed applications eats your hardrives space, and when it is almost full, your computers performance is affected, making it run slower.
You may free some of your harddrives space, by deleting unused programs.
-Click the Start button
-Click Control Panel
-Double Click the Add/Remove Programs
*here you will see all the programs installed in your harddrive, Click the Remove button, then Click Yes if ask by windows, to delete programs you never used