Open and Import

Depends entirely on what it is you are trying to open or import. With files, there's no difference in Waveform view - although logically, importing a file should simply place it in the files list, rather than actually opening it. Doesn't work like that though - importing the file actually opens it. In Multitrack it's slightly different; opening a file will do the same thing as happens in Waveform view - your file opens and you see it in Waveform view. But if you import a file in Multitrack view, it will simply place it in the session's file list and do no more with it. Personally I think that should always be the thing to do with an imported file, and all other file import actions are incorrect, but hey, nobody's listening...

With items in the import list like applications and markers, it's obvious. With raw data though, it's essentially the same as with files, except that you have to specify the missing file parameters.