I've found it useful to have a rear brake for longer rides in hilly places, to give my legs an easier time on descents. For riding in town, however, I'd be surprised if having a rear brake as well as front would actually make much difference to front only. I find my stopping ability is more down to my powers of observation, my reaction time and the friction between my tyres and the road surface. I'm happy with just front for the time being.
I've found it useful to have a rear brake for longer rides in hilly places, to give my legs an easier time on descents. For riding in town, however, I'd be surprised if having a rear brake as well as front would actually make much difference to front only. I find my stopping ability is more down to my powers of observation, my reaction time and the friction between my tyres and the road surface. I'm happy with just front for the time being.