If you want to keep a walk on 4 years and have him develop into a mid level reserve, I wouldn't have an issue with that in the least. I assumed the OP was referring to walk ons who were talented enough to play immediately, and that I am deadset against. But if you want a system where a walk on, with the proper coaching over a couple years with the benefit of a scholarship turns into a serviceable reserve after 2-3 years, I think that would be OK, but can't see too many teams wasting 2-3 years to develop a player to get 10 bench minutes his senior year.