Videos vs. Movies -- The DB UPDATE tab has a checkbox labeled "Movie" which (if selected) downloads video files into the MAME tab's "Videos" folder.
Covers vs. Marquees -- Everywhere I've seen in the MAME world, the term "Marquee" is used, and I had no idea what "Covers" was used for until I saw my cabinets show up there with a theme that shows marquees (SystemArcade...).
Snap(shots) vs. Screenshots -- The MAME distribution creates the 'snap' folder, but The UI asks for a "Screenshots" folder. This didn't slow me down, but I mention it to be a little more thorough.
I searched quite a lot but never found explanations for what some of the folders are:
- Logos - where would this be used?
- Arts - what is this and where would it be used? The MAME EXTRAS package (available elsewhere) has 'artpreview' which is what I've added here, but I haven't seen it used anywhere.