When goods are to be moved around in a relatively confined area, either during manufacture, or to and from storage, mobile trolleys are usually the best solution. But, there's a definite limit to how much one person can push. Roughly, using castors, a man can push 1800 kgs for 1 meter,1200 kgs for 10 meters, or 600 kgs continuously. An average adult can directly lift 16- 18 kgs. Using castors &  wheels increases this to 600-800 kgs, but greater loads require tractive power. If any of these limits are regularly exceeded, there's a clear case for towing.
Similarly, there are limits to what a forklift can do. Basically, it can only move one pallet, or load, at a time. If there is a lot of material to be moved some distance, there's a good economic case for using more trolleys instead of more forklifts. Trolleys are often specially modified to contain loads more safely, or to act as a jig or part of the work holding fixture. The load can be wheeled to a work center, thus reducing handling time and effort. Trolleys can also be matched to the height of a work table, so the load can be slid directly on and off the work area.