A lot actually! In addition to providing jobs to about 65 people in the electric department who keep Stillwater's lights on, the revenue is used to replace or repair transformers and to purchase equipment like poles, wiring, street lights and bucket trucks.
Another important benefit of being a public power community is that a portion of the revenue is reinvested to improve and maintain crucial city services such as fire, police, parks and roads. Since Oklahoma cities rely primarily on sales tax to fund local government services, cities like Stillwater are fortunate to have this additional revenue source.