There’s two things happening with a capo being conflated: 1) Changing the key of a song by moving the nut up and playing the same fingerings; 2) playing your “fixed key” song, that you need to play and sing in a specific key, with different chord shapes, maybe folkier etc.
A capo moves the nut of the guitar higher. The strings are shorter, and hence a little more brittle, and defined, the higher up you go. Any altered “technique” of fingerings is only affected by the tension and width of the neck at the place where you are playing.
You can do it to sing in a better key for your voice. But for acoustic songs a capo can just be a great sound. You don’t use it on a les paul to play hard rock.
Pros may get fancy and use a capo on some strings and not others. But other than that I can’t think of “technique” or expertise that a capo gives access to for a player other than changing keys, or chord shapes.