I used to commute on a fixed gear road bike, with panniers etc. This was ideal. Things change though, and my current commute is a mix of off road routes, which isn't really suitable on a road bike. I'm currently running semi-slicks which just about deal with gravel and mud, on a couple of sections of my commute, but most of it's paved. I do have a canal route too, but that does need off road tyres, and I'm not doing it in winter due to the mud