Just a thought related to this lesson, it seems that power chords playing the top 3 strings and muting the bottom 3 is almost the same as just playing an Em shape barre chord. I find I sometimes press down the high E string instead of muting it, but even with distortion it doesn't sound too bad!
And I guess power chords playing the 2-4 strings (A,D,G - do we count strings from low E to high E or the other way around?) is also similarly playing an Am shape barre chord.
Is it common to switch between a power chord and a full minor barre chord for emphasis in rock music? Or no?