I note some of these issues have come up before - for example: Reducing Size In PDFs - some more problems I find with the PDF exports:
(1) they're large as noted
(2) (perhaps why they're large) they seem to be images either of the whole dashboard (the "tiled" pdf) or of each look (the "single column" pdf). So you can't cut and paste any of the numbers or strings from an exported PDF to another application, you can only copy the entire image (either of the look or the whole thing).
(3) Also there are no links. Now links to Looker pages might not be helpful if the PDF is being shared outside of your Looker users, but external links should be good for everybody, and they're missing from dashboard pdf's.
(4) There doesn't seem to be any way to control colors, fonts, etc. (it's whatever the Looker interface shows online, but this might not be ideal for a PDF)
(5) They're a single loooong page (if there are a lot of looks on the dashboard). Is there an option for a "one look per page" PDF?
If there was some way to export a dashboard either in HTML or a spreadsheet format (for example combine the xlsx exports of each look in the dashboard into separate sheets of a single spreadsheet document) that would at least give a bit more flexibility. Right now dashboard exports really seem kind of broken...