Hi
there are a few differences that you should consider.
1. Weight of the window... If everything is in one window, then comes a time when opening time becomes too slow for the user. And of course, you need to add code to load data content ONLY when opening a plane, otherwise your opening time is going to explode.
2. Type of UI... If you are using plane, you have only one thing visible at a time. With separate windows, you can have modal and/or non modal windows and display multiple types of information at the same time.
3. You can have an independant HF context per window... NOT per plane. Your code should reflect that, if it's not always the case.
As a result, I tend to mix both techniques. I will use planes for all the differents process on one file, by example (browse table, select, create/edit/delete/ secondary process), but I will use a distinct window for each process/file, so as being able to display multiple things if it's interesting/necessary.
best regards
