I feel like we have discussed this before. I also recall the previous thread on this topic going for many pages. I also recall Ithilus_Quo being the primary advocate in favour of the Torrent being Shit Argument. Okay, let us not enter into arguments as to whether or not the unit is more or less cost effective than other options. The question asked was, "who uses them and why?".
So let me answer this question directly. Yes I use Torrents. The reason I use them is because they are the only floating missile bombardment ship in the Aeon arsenal. There are two reasons, and two reasons only why I would build them.
1. As a build power, unit, or eco sniping option.
2. As a force projection tool once I have secured the sea and need to bombard further inland.
I do this because of the vessels two primary strengths. It can accurately deliver dps, and when microed properly can produce devastating attacks against undefended targets. It has the longest reach of any naval bombardment ship. It can deliver pin-point accurate fire anywhere within a huge radius of control.
Now, the thing you need to understand about missile attack micro is that ships waste a lot of shots shooting at dead targets. You solve this problem by changing targets during the volley and sending only the required number of missiles to kill each target. Properly executed you can send those 10 missiles to 5 different targets. Basically meaning that you can entirely strip a T3 factory of all it's assisting engineers in 1 volley. You can also switch targets to shoot mexes. Sending 2 missiles to a T1 mex, and 5 missiles to T2. It is quite easy, for example, to kill off the Island on Setons or Roanoke from stand off range. The other huge advantage you have here is that the missiles take a long time to reach their target. So you can move into range, launch the volley, and be sailing back to safer waters before your opponent even knows that their eco is under attack. For this task I will make a single Torrent and then go back to making Battleships.
In the end game I only make them once I've won navy and defeated coastal defences. In this stage I will change my fleet composition to Cruisers, Aircraft Carriers, and Missile Ships. Which gives me extra reach, and the ability to spam strike aircraft on his doorstep. If the opponent stops this with shields and TMD. You use the carriers to release huge swarms of T1 bombers, or Restoreres.
TL;DR
I use them in small numbers to complement my other naval units. Because, it is one more thing my opponent needs to worry about. It is never my primary force component, and there is never a time when I will base my strategy around this one type of ship. I use it to punish opponents who don't build TMD. I force the counter. Then I laugh when I see shields and TMD popping up everywhere.