Checking Unused Physical Memory Using ST06 (Windows) 

Using the paging mechanism lazy page out  which removes the pages that are not in the working set of an active process, Windows creates permanently free physical memory. For more information, see Special Features under Windows. Therefore, transaction ST06 is of very high value for Physical mem free in comparison to Physical mem avail. Due to a faulty interpretation, the user often increases the number of work processes, as he assumes that there is still unused physical memory available.

A high Physical mem free value has no bearing on system utilization. Physical mem free in relation to Physical mem avail is by definition very large.