Often cited as the mantra of the Tsm product, it is a capability rather than a dictum. The basic scheme of the product is to back up any new or Changed Files. You don't necessarily have to ever perform a "full" Backup (apart from the initial backup of the data) - but of course the cost is Having your Backups spread over perhaps many Tapes (mitigated by Reclamation and Colocation ), which can aggravate Restoral times. But you are free to adopt any combination of Full and incremental Backups as dictated by economics and your Restoral objectives.
Collocation can help reduce the amount of tapes that a systems backup data is spread over by grouping that systems files together, althogh this can cause a high turnover of tape volumes coming back and forth from an offsite DR site if used on offsite copypools.
Reclamation will reduce the number of tapes used to store data in total, but will not prevent the data 'mixing up' over time as it is moved about ro recliam tape space created by expiring files.