Putting them in the speakers just limits the amount of extra things you you have to install, the idea is that in initial setup each speaker goes through a test pattern while the other speakers stay silent, and this gives you position of all the speakers and the acoustic properties of the space they are in.

Though if you also have some extra microphones, then you can do dynamic adjustments on top and even account for people moving through the space so that they do not block sound or even so a stereo recording follows them around.