in competitive programming, people sacrifice a lot of readability, and never write documentation. (simply because there is no time) If you only ever do that - people wont like working with you (and well, you wont know how to work on bigger codebases, use source control, stuff like that)
is competitive programming / solving exercises fun? sure will you be a good software engineer if the only thing you do is solve distinct problems, never working on a complex project that involves a lot of parts, and always sacrificy readability and never write documentation? most likely, no