I'm not super big into MIDI, but I believe it works like this:
[example] You're recording a keyboard part and moving a CC knob on your MIDI controller to change the sound of a VSTi. Now you want to move some notes after you've recorded it. This option will allow the CC messages you recorded with the knob to stay synced to the notes while you're moving them.
I could be wrong.. As I said I'm not big into MIDI. The manual most likely explains this option. If not, try the REAPER message boards at REAPER Forums - Cockos Confederated Forums or just start playing around with it. You won't break anything
thanks man. Just easier to get people opinions that trawl through posts trying to find one little bit of info.
I dont like the colour of the reaper forum it make me ill its all green and grey :-(