Thus, your understanding of the shape can be misled, and your attempts at adapting a pose to something slightly different, or coming up with your own (let alone dressing them up differently) will likely be stilted and wrong in a number of ways - because you're trying to imagine what's underneath without understanding that there is a muscle belly there that doesn't bend that way, or a bony protuberance being an anchor point for other landmarks, and what have you.
Imagine "learning anatomy" from studying a cohort only wearing the ultra baggy styles that are around currently.
You don't have to know all the names for all the parts... but you will probably get better results by learning from the ground up then inferring how the outfits drape over that.
See Kim Jung-Gi demonstrating some of that (the subtitles are even somewhat useful) https://www.youtube.com/watch?v=LVn205YsQhY