TSM can collocate (i.e, keep on the same tape) all files for one node, or
not.  If you tell it NOT to, then a FULL restore can be slow - but full
restores are the exception rather than the rule. A single-file restore will
still be fast.

Not collocating files is good because it lets several nodes share one tape
volume - better use of your storage than havin a bunch of tapes all 10% full
(because the client only uses 7GB and the tape holds 70GB).

Collocating files is good because restores are fast - only one (or few)
volume mounts.

I usually advise collocation on business-critical servers, non-collocation
on desktops and such.