You may sometimes want to set a bunch of multicursors on a lot of lines, where just holding C and letting key repeat do the job is a bit bothersome.
So you mip to select inside paragraph, and use s to set cursors how you usually would with C, but with far less keystrokes

rec.mp4

Doing this feels illegal fwiw, but it's actually super valid for this usecase, where you want to act on a certain column, rather than anything that you can regex match by text.
If you know exactly how many columns you need to match, you could also just ^.{30} or something, but I generally don't know.
Regex is really powerful in theory, really fun to learn how to use it more creatively.