mc. note allocator
I've been following this tutorial on youtube , using mc.noteallocator for a poly voice .
I'm also a bit confused why the right outlet of midiformat is used , isn't this supposed to be solely used for vst instruments ?

midievent message is meant for all objects that can use it.
it was added to midiformat output in earlier max versions,
i think max 7.
vst~ requires this message, for other use cases it is more or less optional and only used because it got added to midiformat some day.
midiformat returns critical messages for utilize multichannel voice allocation of mc.noteallocator. such as how many keys are pressed, midi cc, etc. noteallocator plays the role of [poly] in vanilla Max environment. Although there's a few other ways to create polyphonic structure in mc. environment, this is the most straightforward ways to make polyphony synthesizer with mc.
here's simple synthesizer example I used for the class.