There are a few notable differences between the modes. In MTP (Media Transfer Protocol) the Sansa is seen as a media device, allowing protected (DRM) media, automated album art folders, song ratings, and playlists, since WiMP sees the connected device as a media player. In MSC (Mass Storage Class) mode, the player is accessed directly as a flash drive.
MTP is a virtual mode, or an automated layer on top of MSC, supported by Windows Media Player. Funny thing is, Microsoft configured it to look almost exactly like regular MSC transfer when using Windows Explorer and drag-and-drop transfer.
WiMP is equally happy, as long as the media is not protected (DRM) transferring files in either mode, contrary to what many may think.
The problems surface when trying to do some manual tasks, such as playlist utilities, since these are path-specific, rather than simply filename specific. MTP allows something really cool, though it isn’t explained well. You can right click on a first file, then begin a playlist by dragging the desired files into the new list box that pops up. To the uninitiated, it looks like you’re actually dragging the files into the list, but it’s just the names.
The completed list can be dropped into one of two places on the Sansa, either into the Music folder, or better yet, keep them where they can be found later, in the Playlist folder. It can get confusing, but the Sansa knows the difference anyway.
You can build playlists easily in WiMP too, and they will automatically go to the Playlists folder.
There’s a “wall” between MSC and MTP, in which files transferred in one mode are not visible from the computer when connected in the alternate mode, so files look like they’re “missing”, though the Sansa sees ALL files regardless of transfer mode. This is one of the reasond why many users simply choose one mode exclusively.
Linux or Apple computers generally don’t support MTP mode, so having MSC is quite handy. For the serious propellerhead, there is libmtp available in the linux realm, but I haven’t had the chance to probe into it. I have got to set up a cool kubuntu partition for that, as I really love the KDE interface, it’s uber cool.
Glad to confirm that WiMP does yet another thing in the background, namely the metadata, without changing the source file. As we’ve found, it’s another cool tool that you most likely will not find in the circuitous (code word for confusing as hell) Microsoft help files for WiMP. I just had a feeling that WiMP might be "repackaging’ the file in transfer, since I have some albums with test images that sometimes pop up on test Sansas, and the difference is that I’ve dragged the source files directly to the Sansa rather than using WiMP.