Routing vs Direct Routing

Can anyone explain the difference/reason why there is Routing and Direct Routing in the mixer?

Direct Routing allows you to have to have 7 post fader / post panner Routing destinations.

I see, the difference ist that Direct Routing offers 7 destinations “in parallel” whereas Routing does only allow one destination to be selected.

This probably describes it best in use:-
https://www.youtube.com/watch?v=xiJeIObQSE8&feature=youtu.be&t=1010

The summing mode is also an important factor in how the processing works.

When in summing mode - yes. But it also let´s you switch (and automate!) output routings in Standard mode for example.

Will that be any different from sending to multiple FX tracks?

It is much faster than stting up 7 sends (my opinion), and it is an output routing, not a send. With the send you still have the original dry signal. Of course you can tweak both to behave more or less the same if you want to.