I see this opinion in /r/cscareerquestions a lot and I don't understand it... the people that say this (not saying parent comment is one of then) usually say cover letters are a waste of time and claim to apply to 100~ jobs a week or more.

In my experience, that has never worked out though to be fair I don't even think I can find 100 jobs to apply that I like. I preferred to focus on a few (10~) places and really try to form a connection either through cover letter or Twitter/GitHub/email.