Well I can tell you this. If you using Mono you won't be able to get the full use of your effects. effects always sound better in stereo. You can here the waves switch from speaker to speaker...
Somehow I don't think for now they would worry themselves about panning effects... But you do bring up a good point.
Derik - if you don't have stereo you may sometimes have an instrument come out of just your main left speaker(s)... & you stand there thinking whats going on?
It's because the keyboards signal is being sent to ONLY that left channel. Yes, you could just use the pan function on your church mixer BUT it will decrease the overall volume & depth of sound you could get out of that system.
If you had your keyboard hooked up in stereo you will hear the full sound across both left & right channels. Which means your keyboard will come the WHOLE system - giving it that full sound that some here are referring too.
Also a special note (& incase you didn't know) if you are using Jack or 3.5mm cables make sure you know which are mono & which are stereo. As you can see below - One line = mono. Two lines = stereo.

