The shorter MCT the shorter overall flight time (from point A to point C via point B) is and the better position in the GDS'es (SABRE, Amadeus etc) plus possibly a better position in all sorts of Kayaks etc - especially when you shop by schedule and not by price... (I just noticed Kayak allows you to establish your own MCT and disregard connections with layovers longer than X minutes).
That's a really good tip, btw. Thank you.