Max & Pd are fantastic for incorporating sensors & other physical interfaces, real-time interactivity, routing signals, creating visualizations, & all that. Supercollider is fantastic for generative music & using control flow compositionally.
Csound, on the other hand, is really, really great for creating beautiful & nuanced electronic compositions. The sound quality is unrivaled (emphasis on accuracy over interactivity), the interface is great (plain text, which, as a programmer, I prefer), and GEN routines plus the myriad opcodes allow you to do some heavy, intricate aural spelunking.
As a bonus (& as mentioned by others), it’s highly performant & fairly easy to integrate with other languages & environments (including Max & Pd!).
The syntax is a bit strange, but once you get over that, Csound is an amazing piece of software.