I'm annoyed equally by the space they take up and their presence.
We pulled an old camera out to donate the other day and I popped the SD card in my laptop to see what might be on the card. It was a 1GB card "full" of photos my kid took on one of our vacations. I say "full" because there was a 125mbs of files Finder left wasting space on it.
That's easily 25 photos that weren't taken. What shots did we miss because the SD card was "full"?
A 1GB SD card is likely to be formatted with FAT16. Even a "one byte" file must take up 32KB in the file system because that's just how big the clusters will be.
Have a look of how many repositories on GitHub which include a completely unrelated .DS_Store file: https://github.com/search?q=filename%3A.DS_Store