So when you buy an Adventure, say Dragonheist,.  Do you share it with players?  Or is there no need?   I'm thinking if it's shared some may peak and questioning if better to merely run the adventure and purchase the hardcopy instead.  What's the pros and cons to getting it in dndbeyond? .   

The pros to having it in DDB is that the adventure-specific monsters, magic items, spells, character backgrounds, etc. will be available for your use in the Encounter Builder and Character Builder.

Note that the Campaign Content Sharing toggles only apply to the compendium, not the character builder, so you can keep your players from reading the book while still being able to select items for their characters.

(The only downside is that they can use the search tools to view monster stat blocks, but then that's already going to be the case with monsters from the Basic Rules and sourcebooks you own.)

If you'd rather not risk it, you can purchase just the magic items and such ala carte from the book's Additional Purchase Options, to make them available to your players when they'd gain access to them. Already purchased options are deducted from the cost of the book if you choose to buy the whole book later on.

Another pro, depending on how you play: you can download the maps (or other graphics) and upload them to your VTT of choice, or print them to show players.  (Printing to 1” squares may not be feasible without a lot of work on your end).  I also found the hyper linking to be helpful: especially with the new compendium upgrade that lets you copy the hyperlink to a section heading in a compendium.  THere used to be a third party extension that (among other things) did that, and I made extensive use of it in putting together my prep notes (first in the campaign DM notes, then in Dropbox Paper)