I played out with a wireless for the first time yesterday at church. The guys running the main board don't have a ton of sound experience (but they are learning). I wanted to try wireless because I run back there occasionally to help them out and that disrupted rehearsals. I also wanted to hear how I was sounding in the house mix compared with my amp on stage.
So there are two ways in which, at least for me, wireless proved quite useful. But wait, there's more... I also switch back and forth between a Carvin 5 string (now with the wireless) and a WAV4 EUB, and the wireless brought two more unexpected benefits.
#1) The gain setting on the transmitter made it easy to get the volume on my Carvin roughly equivalent to the WAV4. While I probably won't use it that way, it's nice to have that option.
#2) With the transmitter firmly attached to the strap, switching basses between songs (taking off the Carvin and putting it on the stand, then hitting an A/B switch and a different GT10B patch) is less hazardous - there's no cable to trip over or get yanked out.
While I'll still be keeping a good ol' fashioned 1/4" cable ready to swap in at a moment's noticed, I actually found the wireless to be a practical tool in my setup. And besides all that, freedom to roam a bit without worrying about getting tangled up is kinda nice...