The saying "quantity has a quality all of its own" definitely holds true for running as well.
A large part for me is that I have learned that it sometimes takes me a while to really get into a flow. The most extreme case I can remember is a time I went for a 21 kilometer run and did not feel like I really got myself in order until about the halfway mark. That is the extreme case, but five kilometers is not unusual at all.
About two weeks ago, inspired by a friend who is in a really good running flow, I made a point to make myself run ten kilometers instead of my recent regular of seven or eight. I have kept it up since then, and even on the second and third runs it felt like I had broken through a barrier to higher speed and better flow.
I think much of that is down to those few extra kilometers. On days where it takes me five kilometers to find my flow, the majority of a seven kilometer run will be the boring non-flow slog. But now that I extend it by just three kilometers, I get at least half the run in the flow zone, where I feel better, enjoy myself more, and I suspect also run a little faster and better. All those positive things build on each other, plus the added distance adds that nice little glow of good physical tiredness afterward.
I feel better all day, all through the week even, thanks to those few extra kilometers.
Three kilometers to a better person.
Not a bad deal.