Jan Heine did a test in Bicycle Quarterly a couple years ago that showed, for comparable tires, fatter was not slower. (Comparable meaning similar in weight, tire thickness, and construction).

Two problems with that conclusion. First, it's hard to get lightweight tires in 32 with high thread counts. Second is that fatter tires often have thicker rubber, which is good at least for a commuter, because the thicker rubber lasts longer before wearing out and prevents flats.

If you try to hustle in early to make that important meeting with tires that aren't really worn out yet, Murphy will see that you get a flat. That gets you to your meeting late and dirty.