Most people when they first get into speaker building do not realize that how far apart you put you speakers can actually affect it’s sound. One those ways it affects it (negatively or positively) is with lobing and polar response. Stated differently, the correct spacing will help fill your room better with sound. This is especially useful when making and designing an MTM. It may seem like what he designer choose were arbitrary distances, but they are actually very well thought out calculations. Here is a great article that goes into detail about this and even helps you figure out speaker placement.