A static day off in an otherwise rotating schedule increases the quality of life for a retail worker considerably. It also happens to be a day off that many of your friends and family are also likely to have off, rather than often having random days off during the work week. A retail worker might actually be able to maintain a normal social life with a recurring Sunday off.

A lot of (most?) hourly work has employees permanently on call for shifts the next day or even same day.

Knowing which day you’re off lets you plan.

If you have a significant other and/or kids, it significantly raises the chance that all have a free day at the same day.