Being able to interact with the regular customers who bring positive attitudes with them, and that is what makes the environment a better one for the employees.
I enjoy it when my regular customers come by my section to pick up their regular items and are always happy to see me, because I keep my section well-stocked.
Generally, the employees that have been there a while are more likely to do their work to the best of their ability and then some. It means less stress for the team overall when everyone does what they are assigned efficiently.