Any industry will use it for freight. In fact, you technically don't even need stations, they'll dump freight right on to any tracks that border them, but they work a lot better with stations. Ground rail is also one of the cheapest ways to move a lot of people. You can also park a car at a train station so people who don't like riding buses can still use it, and if you put a bus stop next to a rail stop then pretty much everyone will use it. People tend to ride the trains to industrial zones.
I'm not familiar with el rail because I don't use it much. I bet the above ground stuff is cheaper to maintain than the subways, and there's also the whole aesthetic effect.
I also like to use ferries, which although they're not very fast or high capacity, they do help alleviate some congestion on bridges. Unlike bridges people can ride one ferry to any other ferry stop. People can also ride the boats between cities.
At the end of the day it's all about redundancy and variety in mass transit. I use pretty much everything except el and monorail.
