This mod is a HUGE step up from the default carts. Aside from having bigger, nicer-looking transportation, the trains can run automatically no matter where you are. I find this very usefull in creating large worlds where walking everywhere is extremely tedious to say the least. I can set up trains that run to various places, and getting where I need to go takes a fraction of the time.
It also includes advanced train control and signal systems so that you can have multiple trains running on the same stretch of track, while avoiding crashes. Also, when installed alongside the Mesecons mod, you get more features like detector rails, which can be used for making station lights, and also can be used for programming more complex train control systems (I have yet to dig into all that myself).
There's a slight learning curve for track placement and the signal system, but once you get the hang of it, it's logical and straightforward. Also, the trains look great!
For building complex signaling systems, there is a feature designed for the purpose. LuaATC (Lua Automatic Train Control) allows running Lua codes to control trains and turnouts.
The reason you should use LuaATC rather than Mesecons-based systems is:
1. Using fewer spaces. Hiding Mesecon wires is always a tough task. LuaATC put all the codes into a single block/track.
2. Work with interlocking systems. LuaATC could set routes on signals that would allow detection of the section state before allowing the train to go.
3. The most important difference: LuaATC works in unloaded chunks, but Mesecons does not. In Mesecons-based systems, trains may not obey the routes if the Mesecon systems are not loaded.