I don't know why anyone would categorically choose to do or not do something. To me, it's all about context, situation. Most of my commute takes me through busy city streets with lots of slow moving traffic, where I am passing said traffic to my left and parked cars to my right. My main concerns are getting doored, which happened to me when I was on a motorcycle once on the same route, and left-turning traffic through intersections when it's dark. That's about it. I've been squeezed by trucks and buses (not very often), but the traffic moves so slowly, that there's always a way to deal with it. Getting trapped next to or in front of moving traffic is actually one of my least worrisome outcomes -- drivers can then actually see you and normally aren't rabid ******** out to kill you. You just make eye contact, get out of their way as quickly and predictably as you can, wave to apologize, and all's well. The other thing I always keep in mind is the difference between traffic patterns I know and patterns I don't. I am able to be much more aggressive negotiating routes I am familiar with during times of day I normally travel there. There are then countless "hot spots" that I know not to get too crazy with and also places where I know the traffic light timing, road conditions, and pedestrian behaviors well enough that I can approach them with some gusto. Again, everything is an exercise in risk management. No behavior or philosophy will guarantee 100% safety. Know your limits and remain vigilant no matter what you do. Ride safe!