I personally use it with my Babyface Pro to monitor without latency and with some reverb while recording. Monitoring through software (DAW) adds noticeable latency. But I bet there are a lot more advanced use cases.

Using it as a flexible OSC controlled digital live mixer and recorder (in combination with some hardware de-essers). It’s doing a pretty decent job, though it would be great to have some more sophisticated dsp (especially soft knee control on the compressor, faster attack / limiter, more bands on the EQ).

Beside other things, I use TM together with Digiface USB as intelligent ADAT patchbay. I use few digital effect processors and may easily route signals to them and between them. Just by loading preprepared snapshot the routing (effects used, order of effects, signal(s) to be processed by effects...) may be radically changed.

The eight TM FX Snapshots / routings allow me to switch between 8 entirely different use cases and
automatically restore all needed settings (gain, submixes, loopback).

In addition, the Matrix gives a complete overview over all submixes at once.
In the normal submix orientated view you get the submix of the selected HW output.
You can see the submix according to the fader position in top and middle row (HW inputs, SW playbacks (audio from PC)).
Of additional help is the small button "Sub" which only shows those channels that route audio to the output.
But everything according to this one HW output.

Matrix view shows you on the "x-axis" all HW outputs.
And what you see in mixer view usually in top and middle row, you see now in a vertical orientation.
Therefore you have here a complete overview of your routing for all HW outputs.

Additionally useful are two additional functions, you can
- hide not needed channels in "Channel Layout" which is applicable for all snapshots
- store up to six of such "Channel Layouts" for showing most important channels of a device or for a certain use case

Both in combination gives you a phantastic overview in mixer and matrix mode.

To get an even better overview you start a setup best from scratch and delete all routings quickly in matrix mode
and implement only the needed routing for e.g. monitoring and what is additionally needed.

This gives then the best overview in mixer and especially in matrix view if you only see those things that are really needed.
After that you have also a much better understanding about routing in general and TotalMix FX's logic.

At the end it boils down, to two simple things
- Audio Signals coming in from devices that are connected to your inputs
- Audio Signals coming from the PC

Due to TM FX's logic design you can decide for every HW output whether you want the audio signal
- from the HW input with the lowest (near-zero) latency or
- from the PC with higher latency which depends on buffer settings and whether you have full RTL or half of it
  full if the signal came from a HW input, half if the signal originated on the PC (e.g. from a virtual instrument)

I do not know any other mixer software which presents this topic in such a clear, logic way
and offering so many useful functions for operation and which works flawlessly.