why do you need 2 channel change options?

Could somebody please tell me, why you need the two different channel change options in the expression map?
what is the advantage to go to another channel by relative channel change compared to absolute channel change?
For me just one of these two options covers everything - why would you need both of them?

Suppose you want to use the same expression map for several different instruments, or several instances of the same instrument.

The first one plays on channels 2 and 3, the next one plays on channels 8 and 9, and the last one on 13 and 14.

You probably want a relative change of +1 or -1 to switch channels, not three copies of the expression map.

On the other hand if you have a huge VST instrument that uses say 10 different channels, you might as well make it use its own midi port, and always use fixed channel numbers 1 through 10.

Got it…thanx a lot Rob

So let’s say I have playing technique ‘ah’ on channel 1 in voice 1 and playing technique ‘oh’ on channel 2 in voice 2. I create a playing technique which I call ‘switch’ with a relative channel change +1. So I get a simultanious change from from channel 1 to channel 3 and channel 2 to channel 4 when typing ‘switch’.
Is that right?
Instead of typing 2 new playing techniques (on channel 3 and 4) I just type ‘switch’.