It may not be worth adding the extra stop unless its way out of the way distance wise. Sometimes adding more connections brings the price up and puts you more at risk of not making it to your destination in time should you not leave enough times between flights in case of delays.

For instance according to the great circle map, BOS-LAX is the same number of miles as BOS-MSP-LAX

BOS-MSP-LAX is only 48 miles longer than BOS-LAX so its not worth the extra effort and risk. Also with TSA tax difference its can be a wash or more cost per miles than non-stop.

One I really liked that United killed a while back was BOS-IAH-SFO-PHX, backtracking through SFO added a lot of miles