My guess would be that it's a precursor to an Em->F or Em->Am transition; i.e., if you wanted to transition to a minor mode convincingly from C, you'd toss the

My guess would be that it's a precursor to an Em->F or Em->Am transition; i.e., if you wanted to transition to a minor mode convincingly from C, you'd toss the Em (or even E7) in there before hitting Am. Example: Santeria by Sublime (I-III-vi-V)