The most important structural role is in tying together a sequence of visual images and/or a series of dramatic episodes, narrative voice-overs, or a list of product appeals. This is the function of continuity
Historically, the use of music to achieve greater continuity originated in film music
-- where one of its functions was to smooth out sequences of discontinuous scene changes or edits. The music is used to mediate between disjoint images. Thus, advertising music can be employed as simply an uninterrupted background -- what has been dubbed "gravy train."