A few words about the way that MMB works with large folders.
MMB lets you set a root folder path, and shows the subfolders under it. You can choose whether clicking on a folder shows the recursive contents of that folder, which can be very useful.
For paths with only a couple hundred images, everything will happen fast enough to not worry about details.
Things become slightly more complicated when you are dealing with folders containing thousands of images.
In this case, clicking on a folder node (or the root folder note), can take several seconds (minutes even) to scan the recursive contents of that folder and all of it's subfolders.
After scanning is complete, exploring and clicking on any of the virtual date folders will NOT trigger a need to rescan the directories, and so should be very fast to drill down into the virtual date folder.
HOWEVER, clicking on a sub-directory currently DOES trigger a re-scan of that subdirectory. Because of this, drilling down into a subdirectory and then BACK UP to the top node, or refiltering based on keywords, could present some annoying delays.
The benefit of this is that the program is happy for you to jump around without having to first rescan the entire path (aborting the initial scan, etc.)
What I will probably try to add soon, is a feature that will be a little smarter about rescanning -- so that if you have a giant folder you are working with, AND you let it do an initial completed scan of that folder, it will thereafter (on the same run) not have to rescan as you pop in and out of subdirectories.
That may be a little confusing.. To summarize: Each time you click on a subfolder in the DIRECTORY tree, or change the keyword filter, the program rescans that directory; each time you click on a node in the virtual date tree hierarchy, it does not rescan files, it simply filters them to show only those from the matching date.