My attitude toward single elimination playoffs varies with the
type and circumstances of the tournament. For any regional qualifier
or prestigious title, certainly I prefer double elimination, or if
time doesn't permit, the advantage/shootout system we often use at UTC
(if two teams square off in a playoff, the team with the better record
and/or head-to-head gets as one-game advantage; if the team with
advantage loses to the other team, the tie is resolved by a 20-tossup
shootout.)
However, for our high school tournaments in particular, single
elimination playoffs seem to be preferable because (a) they allow us
to have more playoff teams, especially useful for a large field, and
(b) they keep the tournament shorter, which is more of an issue for
the high school teams. Single elim also works for smaller trash
tournaments, and sometimes for collegiate tournaments where time
and/or question supply make it more desirable.