I have just started considering this myself recently as to whether or not to carry at all. I only own one pistol which was purchased for home defense and recently decided that I want to start carrying to provide safety for my family outside of the home as well as inside. This thread has been very helpful to me as we'll since I didn't realize there was so many conflictions that can occur over the decision to carry.
On a side note, the fact that you live in Philadelphia alone is reason enough to carry 24/7. I live just outside of the city, about 20 mins away, and I am planning to carry all the time myself. Funny how a newborn shifts your views on life.