Then it's timing again. If for some reason a supplying train has been delayed, there will be little or nothing to load when the other train arrives. If the loading train isn't set to wait for load at all, it will run empty or half full and lose money. Unlike the deadlock situation, the game won't warn me when this happens. If one sets a longer waiting time to be safer, the station will eventually become crowded with goods, causing potentially bothersome warnings.
Pak set differences might have something to say here, though. With pak64, it's almost absolutely necessary to have trains running fully loaded in one direction in order to make a profit. A few extra platform tiles on the other hand has never ruined my economy. I think I have just a single freight train that doesn't wait for 100 % load, no matter how long it takes. That is a small and cheap shuttle train between two nearby stations/factories, where interconnections cause goods to flow both ways. In this case, space restrictions make it difficult to add an extra platform in order to have two trains, with one waiting for full load at one station, and the other waiting for full load at the other.
A pak set where trains are profitable even when not full, and where platforms cost a fortune to maintain, the situation would be different.