There are other uses where you direct each channel to a different instrument, but this doesn’t make it wholly necessary.
If you do decide you have a need for MMO then I would consider Unify as per @kpsiegel’s post. There is quite a good video demonstrating midi routing Instacomposer through Unify and several instruments in Abelton Session View.
I’ve just started looking at this with the demo version, but it stops working after 15 minutes and Ihave to reload it (grrr!). It does seem quite easy to use, but we shall see.
BTW if you do decide to buy it search for discount codes: I found one today giving $15 discount