When the difficult aspect of a dance is the transitions rather than the
formations is that not the time to do a quick walk through by a first
couple who KOWNS the dance? I could be wrong, but I still think the
main reason walk-throughs are avoided so vigorously has more to do with
the conitation of "beginner" rather than time.
There will always be people who get up to dance who shouldn't. Give the
others a break and don't waste time just briefing complicated
transitions or unique formations. When this is the problem I think the
dancers who fail in the set are often very experienced dancers who
"know" they can do a dance from a briefing and haven't bothered to do
any homework. As I said before, if you take the time for briefings and
walk-throughs out of the break time the total time wasted is nil. (Let
'em rest while they listen.)
Summary: formations should be briefed, weird stuff should be shown.