Outdoor gigs – unless they’re small and intimate and the audience is likely to actually listen. The sound of a choir outside doesn’t carry well, so singers tend to push and become vocally tired very quickly.
Sometimes at outdoor venues, well meaning souls have set up a single microphone to amplify the choir. I think we all know how that story ends – especially if the microphone is directional. One moderately strong alto in the middle of the choir can totally obliterate the sound of the rest of the group.
The other problem with outdoor amplification of a choir is a cultural one. As soon as people notice the amplification, they feel that the performers have given tacet approval for the audience to tune out or chat – that they’ve given up expecting anyone to be quiet and attentive.
As a solo performer I kind of enjoy doing the background schmoozy wallpaper music – it’s so easy on the nerves. But when a choir has done a lot of work on tuning, balance, blend, dynamics and the whole emotional, entertainment package, it’s very unsatisfying to be completely ignored. Choirs don’t sing well under these circumstances (especially if they’re having trouble hearing themselves) which means that they’re rehearsing singing poorly.
So the moral of this story is – only if you need the money!