I have mine setup to auto delete if I have not seen them in 90 days. All of our machines should login in that period. I also use the report for Not seen in 30 days to see what machines are not being used. This is for a network of about 2000 machines at 85 locations.
I also have some reports that track duplicate computer names and duplicate Dell service tags, as my IT staff likes to move/replace machines without letting me know.