For as long as I’ve written this blog, I’ve advocated treating your long runs as rehearsals for the big day. Hone in your nutrition, pacing, and even clothing strategies while it doesn’t count, so that there won’t be any surprises when it does.
Actually, I think you should go beyond just rehearsing: instead of just “sticking with what works,” use your long runs as a testing ground for potential improvements. I truly believe most runners have many minutes of improvement just waiting to be discovered, but instead they fall into the trap of never varying from a routine that works well enough.
Up until I started training for a 100-miler, though, I hadn’t actually done any of this.