I run CCleaner before a Defrag. Getting rid of a multitude of temp files, internet history etc can release a load of space and cut down on lags.
Also, if the PC is reliable, CCleaner provides a simple process to delete all but the most recent System restore points and shadow copies. This can release mega amounts of space on a well used hard drive. Often that alone is enough to speed up a machine. (Get your download from Pirifom)
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