I need to know how long you should keep for example user statistics or all of them going before cleaning out, the reason is when we do a back up it takes forever and without it or about a months worth of stats is fine but any more reallt takes awhile.
Also by leaving all stats in and never deleting out does this cause a high cpu load if the ips saved are used by them or can it cause high cpu load
I personally remove the stats about once a month to keep the DB from becoming bloated. You may find It beneficial to keep them available for a longer period of time, only you can decide this. Although, makes no sense at all to continue storing them if you don’t actually utilize them! 
I cleared out and deleted about 100,000 bytes which is alot but will this cause server to bog down at times