No disrespect Grendel, I did a wedding over in Jersey and the lighting was so bad at the venue that people using p&s were getting orange skin tones. Looked like a sunbed convention! Even on AWB my cameras were struggling and the last thing I need when I've got 100 shots of the ceremony is to start having to WB each and every one. I know you can do them as a batch but mixed lighting at these venues is often a pain in the ****
Which reminds me, I have a venue to go and scout later. I'll take my camera and check the WB in advance so I know what I'm going to have to take care of on the day. In the room where the bride will be getting ready plus the ceremony venue.
If it's close to a standard preset or the camera gets it about right I know I should be OK. If, like the Jersey venue, it's all over the place then at least I'll know I'm in for a day of custom white balances.