Please understand the difference between pleats and creases. Pleats can be used in a lot of placed, including shirts and jackets, to add fabric strategically and improve range of motion. They do also create a visual effect that you might or might not like in certain contexts. They were, in fact, popular in the 30s and 40s, and became less common in the 2000s in 2010s, particularly in tailoring in the wake of Thom Browne's schoolboy aesthetic. In more recent years, I've seen a lot of sreetwear brands try giant, single pleated chinos. Pleats are generally not formal or casual. Creases can be good or bad -- a wrinkle is pretty much just an accidental crease -- but they are *absolutely necessary* for dress pants, and even for dressy chinos. Certain casual styles also utilize a crease; particularly, in some westernwear contexts, starching and pressing a crease into your bootcut jeans is a fairly common move that some people love. Denim usually doesn't hold that crease well, though, so yo...