Cover letters reduce in value as the size of the organisation increases. When applying for large companies with HR departments I’ve found they don’t really get read because piles of CVs are what gets passed around, but I know for a fact my cover letter is what got me into the interview for both the early stage startups I’ve worked for - when you’re starting as developer number 1 or 2 founders really care about who they’re hiring, and a good cover letter is what allows you to frame the CV in light of the company. For example my current job is with a company that does IoT based home security - a skim of my CV at the time would have been completely unimpressive in that context, but the cover letter allowed me to go into some detail about the fact I’ve been done home automation and electronics as a hobby since before I even had a job.
That's a reason, for sure. But I would say that I have become very cynical about this type of reasoning for the following reasons:
1) If you are interested in working on interesting technology, and the idea is that a traditional corporation provides only soul crushing but possibly more stable/well paying work, then I would simply say its better to have a side project instead of working at a startup, because they are unstable.
2) If you are interested in doing work that will change the world, be aware that if you aren't the boss of the startup, then you can be gone in a second because of profit reasons. Better to start your own non profit like Watsi
