I couldn't find a reference to what should be in the boxes in the front page or what stats they are set up for. Are they empty for a reason?

I searched here but didn't see a thread that talked about the fields on the export character sheet. When would you use a 8+prof+bonus stat other than spells, which is already in place? why is it on the front page?

I can't say about the character sheet pdf, I don't use it, but there are a lot of features outside of spells that use Save DCs like Monk features, Fighter Battle Maneuvers, and such. There are also some feats that use them too. 

Thanks, I guess it is just an easy place to put those items, but they are up to the player to decide which goes on the front page. There should be some explanation or an example of a someone who uses the export. 

I use it because I don't have good WiFi access where I play, and using my phone to look at the character sheet is annoying to me during a game

so... then what would go into the slots tho? a number, a stat, etc. surely it's on the irl character sheets you can get, or somewhere on the dndbeyond site when you hit view on the my characters tab. if not, why would it be on the sheet?