I think you're asking how many client backup or archive sessions can run at one time. The legal limit is defined by how many client licenses you paid for (Query LICense). The number, and imposed workload, can vary depending upon things like MAXNUMMP and RESOURceutilization values.
The overall approach is to spread out client sessions as much as possible, to avoid overcommitment of resources and thus better backup performance for the clients, allowing also for separate time periods for db backup and expiration processing, which are too intense to be run at the same time as backups. Refer to the Admin Guide manual or TSM Concepts redbook for background. Richard Sims