Sharing screens rather than sharing applications
When sharing the screen, in fact the screen is not shared but the application is shared with the other side. It means, if the host user drags other application over the shared application in that screen, the guest still sees the older application not the one dragged over. Every time, the host should stop sharing and re-do sharing if they want to share a new application.
Max K commented
For larger sized monitors this woudl be a good idea as well: for example the choice to share a 4:3 or 16:9 full HD portion of your screen rather than the whole screen or just the app.