Hi! I think this should be done by LO and not by the user. I often use Impress during theatre shows with timed animations, etc. and files are sometimes around 1 Gb. Recently (ver 6.3.x Win10 4Gb RAM laptop, internet disabled) either it did not respond to a click (had to do it twice or more hoping the right slide would appear) or it focused on the working GUI covering the presentation.
+1 from me
+2; that would obviously be useful. Automatic saving should be invoked the very last time just *before* going to presentation mode (if there was a change at all).