I'm not sure what you mean by "launch". In this case, we're just
talking about sitting in the office doing the oral. It is such a HUGE
task for me as a CFI to get DE, student and airplane in one place at
the same time, it would be helpful to at least get the oral done while
the student and DE have the schedule available to do so, even if the wx
prevents flight. The DE can always issue a notice of discountinuance if
the checkride cannot be finished that day. It's too bad the FSDO sees
it this way.
Many DE's are scheduled 30+ days out. Having to reschedule an entire
ride (vs a 1.5 hr flight) can push the student out a month or more.

-Robert