Compression can be a bit mysterious and as most of us got into modular to "wiggle" knobs and be hands-on, it can be counter-intuitive to have a module in the rig that's a "set and forget" style thing.
Compressors can be used on any instrument, submix, or the entire master bus. In this video, Alex quickly demonstrates using the MSCL while it is patched in the Master Insert section of the performance mixer, processing the entire mix. You'll get to hear what too much compression sounds like and then get an example of a nice starting point to set the MSCL's parameters for master bus processing.
Compressors are best set by using your ears. You can get an idea of where to start from this video and see what's happening by looking at the LED, but it you will likely need to do some adjustments to the Comp knob to dial in a good sound on your mix. TBH, I left the comp knob a bit high in this demo and would likely use it a bit lower in a real-world scenario.