There is no way to do a partial Send/Receive, and I’m sorry to disappoint the user, but I do not imagine it would become a feature in Paratext. Opening up the possibility of only syncing only part of the project would introduce all sorts of merge issues when (not if) somebody were to forget to sync the whole project.
If you think about the translation process, or the process of working on a document on your computer, the work is in a constant state of “unfinished” until you actually publish it. I think I understand where this user is coming from, but it is just the safest and best practice to save early and save often. Saving locally on the computer is good practice. Doing a Send/Receive often then gives you the additional ability to save a detailed history of your work on the Internet, a USB Drive, or other location. The danger of waiting until they are finished (with any task or stage) is that they could lose work if their computer crashed or something. Doing a regular Send/Receive helps ensure they will NOT lose a lot of work if their computer crashes, is stolen, etc. If they only did a partial Send/Receive, while waiting until a different part of their work was indeed “finished”, it could be days or longer before they are finished. Should their computer crash or be stolen, etc, they could lose days or even weeks of work. It’s not worth the risk.
Paratext is very good at distinguishing what edits were made, when and by whom, and merging them all together. If the team has allowed more than one user to edit the same chapter/book, it is very important for them to be in good communication about who is working where so they don’t accidentally edit a book/chapter that another person was in the middle of editing. There have also been issues with Paratext having trouble merging properly when people wait too long between Send/Receives (usually months).
If this user is concerned about other people seeing his work, I would encourage them to communicate to others that they are not done. But they should still do a regular Send/Receive, at least once/day, and more is better. I have encouraged people to do a Send/Receive at these times:
To start the day
Morning break
Lunchtime
Afternoon break
To finish the day
As well, it would be helpful to do a Send/Receive at any time they complete a major task (for example, finish a chapter, consultant check of a chapter/book, etc).
Obviously, whatever is reasonable for the user. But at least once every day they are working is important. If accessing the Internet is an issue, then have them do a regular Send/Receive to a portable USB Drive throughout the day/week and do an Internet Send/Receive when they are able.