I am 6'1" and stocky. In a 17" wide economy seat I am likely to contact my neighbor with my hips, elbows, and shoulders. In a 31-32" pitch seat my knees are usually wedged against the seat-back in front of me. Getting an upgrade means a lot to me because of my size. But plenty of people who are significantly shorter than me appreciate upgrades, too. My DW and MIL are both about 5'3", which is plenty short to fit in economy, but they have leg problems that make it painful for them to sit with knees bent for long period of time. In an upgraded seat they can stretch out their legs and tolerate sitting for a few hours. As a result we all purchase business class tickets whenever the price premium over coach is reasonable.