For XC, I have my guys do a grand total of zero tempos over the summer. Seriously. Their very first tempo of the year is after our first meet. We are a pretty "delayed" program in that sense. I use marathon-pace stuff over the summer instead. After they build up into peak mileage they will do one every single week until after our first meet. That gives them about 8-9 sessions before we move out of the base phase and into the "pre-season" phase. Most of us consider the season consisting of the two main invites in October to acquire at-large points to nationals, so September is still a transition month.
I do the same thing for track in the winter, except we ditch the marathon pace runs a lot sooner towards the end of indoor. Our indoor season is comprised of those type of workouts, hills, and using races for training in order to shift us into outdoor. People still PR off of XC fitness and this long aerobic stuff. It hangs around through December, January, and into the very start of February.
You can look up for yourself all the multitude of physiological/psychological factors of marathon-pace work and how it benefits you. It is long, so it works well with XC and 10k distances because it too is one long grind in of itself. It also is at the end of your aerobic system, so it allows us to segue nicely into the next stage of taxing that system: tempo running. The best training plans are progressive ones and this pace helps with progressing us to the next stage and not start it too soon. They definitely feel ready and usually crush tempos once they get implemented. Besides, too much tempo running (which a lot of bad college teams do) get diminishing returns after awhile.....both psychologically and physically.
I could post a sample of a cycle if you would like, but I think the biggest thing about what separates good teams from bad ones is the timing of workouts and how you actually do them. A lot of coaches have good training plans but they, and their runners, don't perform them correctly even though they think they do.