Post offices may be many, but their opening hours make it essentially impossible to visit them if you're working. (Unless you want to visit during lunch break and take whatever your received home on your hour-long commute.)
i've received many packages at the convenience store but not everything is shippable there. My local 7/11 just installed a set of shipping lockers so maybe I can receive more stuff without being home. On the hand it's one reason to opt for an apartment complex that has a way to receive packages.