Always roll tape.
Once, I was asked to play some pretty quick unison lines(I shedded the part for 2-3 days...it was still 50/50 whether I could nail it).
Anyway, the night of the overdub, I ask for a run through...as in, 'Don't roll the tape'.
Needless to say, I nail it & it's not recorded. After takes 5-6, I give up & TMK, the tune was scrapped.
