Lighter is probably better, to be sure. Less mechanical stress per step. Faster generally means less steps per mile, and being lighter often means being faster too so it's a double bonus. Maybe I could wear shoes twice as long if I lost twenty pounds. But I think we all know by now that weight is more affected by diet than exercise, so there are a lot of us "Clydesdales" out there.

P.S. For any who don't know, "Clydesdale" is a real running term at least in the US. Many races let men over a certain weight (e.g. 185 pounds) register in that division instead of their normal age group, with its own leaderboard etc. "Athena" or "filly" are slightly less common equivalents for women.