It's the day I became a fast lens obsessive and realised that while the f2.8 might be fast outdoors, in a pub in Walthamstow at night time, it can be more than simply a disappointment, it can also be an utter fail. The 24-70mm might retail at £1,300 and have that lovely gold band, but it was the humble 50mm f1.4 D at £229 that saved my butt that night. Without that lens, I might well have walked way empty handed and how embarrassing would that conversation have been?
Moral of the story: if shooting indoors, assume the lighting is going to be bad, really bad. Plan accordingly. Take the fastest lens you have. You can always stop down. One of the few times in photography where expensive is not better.