This video helped me a lot understanding what the motion sequencer is.. Its part of every performance..

Every of the 16 tracks gets input from a keyboard part..these Notes are either controlled by an ARP, changing the midi pattern...(up to 8 channels can have an ARP)

Then there are also 8 moition sequences that can be assigned to a totall of 8 channels. Every motion sequence consists of 4 lanes.. a lane is controll signal that changes with time.. an example of such a lane could be as simple as the volume raising to max at the beat and then slowly going to half level at the offbeat..

There is also controll signals like footcontrollers and assignable switches that have direct influence to the sound, but thats more part of the soundgeneration..

But there is also envellope following, and this is what makes the Montage incredible flexible.. you could make the beat of the instrument (as in BPM) follow the kick or snare of the drummer.. but you could also assign it to follow a keyboard part, i.e. if you are playing piano, the beat should be able to follow your tempo, slowing or going faster if you speed up the tempo..

But thats it.. the motion sequencer is an advanced form of realtime accompaniment, if you want to compare its functionallity to something you would use it like some use Karma on the Kronos (tough it has very different mechanic then Karma and way less advanced)