OBMM has a feature to view BSA files or something like that which Wrye Bash doesn't have.
What does this feature do exactly?
A bsa file is simply a compressed archive of resources (meshes, textures, sound, etc.). The BSA browser lets you see the content of a BSA file, lets you unpack certain files from the bsa file, or unpack a complete bsa file. Unpacking single files was useful for me when I needed a modified version of two menu files for one of my mods. Unpacking a complete bsa files was useful when I piffy'ed my meshes. But the BSA functionality is not average mod-users will need, except for unpacking and repacking your meshes bsa in order to piffy'ing them.