in almost every software, the shortcut STRG+S is used to save the currently selected/active file. When I open an asset in UE4 and press STRG+S, every single file (!) is saved instead. This is not only unexpected, it’s really dangerous . The ‘save all’ command should have a slightly different shortcut like STRG+SHIFT+S.
I think ctrl-S for save all is convenient, as I more frequently save all my files than just 1, so if anything ctrl-shift-S should save the current file.
CTRL+S for saving the currently active file is just the convention for all other software with different files in multiple tabs that I know (Photoshop, Visual Studio, Notepad++ etc.).
The good thing is that you still get a warning if you attempt to close the project without saving the other files.
No, UE4 always uses the up-to-date files for preview. You only have to save for running it as standalone. Otherwise you wouldn’t be able to experiment without making a copy of your project first.