The absolute most advantageous use case is mobile/portable recording/mixing using hardware: bring your favorite hardware with you on the plane to wherever you’re working. 19” can’t compete with that.
Next is space-constrained work environments where having 19” racks is problematic. And/or grounding issue simplification advantage—advantages unique to the space one occupies.
There can be an economic advantage as the power supply is amortized across the collection of units.
Finally there are advantages of specific pieces which only exist in 500. There aren’t many of these though to be fair. Most of what is available in 500 is also available in 19” or in some cases as a pedal.
The overall advantage of 500 over 19” in this area is perhaps in flexibility for the given space. 500 is 3u high x 8-11 modules depending on the box you get. If you were to get 19” gear in that same space you have a choice of 1-3 manufacturers whereas with 500 every slot could be a different manufacturer.
If someone is unconstrained in terms of space and also has no mobile element to their work then 19” would likely make more sense. Maybe a small lunchbox for the unique items in 500 that a person likes.
Once any combination of space or mobility come into play 500 series becomes an attractive option. With things like the Cranborne or Titan lunchboxes additional economics and functionality start coming into focus as well in terms of workflow and saving money on cabling/patchbays.
Sonically there’s not much 500 can do that 19” doesn’t also do. But for many great utilitarian items the reverse is also true!
