All above is great info. Andreas is right about higher resolutions used for line art. I wanted to further that comment with the reason why print images need to be certain dpi, and possibly fill in the blank where your employee used to be.
Originally, offset printing or web press were your method of printing. Your computer images were output to film with a line screen of lines of dots, or solid lines which are measured in lpi (lines per inch). The minimum resolution for any image that does not appear pixelated when printed is 2x the lpi. Since web press printed at 100 lpi all images output from computers had to be at least 200 dpi. Offset presses started at 150 lpi, so your images had to be 300dpi. Nice magazines like vogue or gq, or sports cards. We’re 200lpi. And required 400 dpi. (Whew. Hope you’re still awake)
Lastly, when your images, text, and everything else we’re converted to film (to make the metal plates that wrap around the drums on the printer) via post script, the resolution of that film was 2450dpi. So anything that needed to be crisp and sharp, like a fine line or (God forbid) rasterized text, needed to be at least 1200 dpi on up to 2450. Anything higher than that was wasted effort since it would not improve the quality.
Hope this helps.
H