You see them everywhere but rarely pay that much attention to them!  Except of course when you need one!  There are alot of uses for portable toilets.  Frequently there are dozens of them lined up at large event and concert locations.  Every construction site needs to have them in order to comply with curent code regulations.  Parties and school activities have them to supplement the indoor locations.  Campgrounds and military locations also use them on sites.  In areas where a natural disaster has struck, you will see these toilets being brought in to provide assistance as rescue workers and others help get the area back on track.