When playing Alegrias in E, the B7 chord resolves to E. If you precede the B7 with a C chord you get an interesting sound (basically a Substitute Dominant, if you speak Jazz) that you can use in lots of ways to spice up your compás.

A nice strong Cierre por Alegrias that includes a very important Dominant voicing that every flamenco player needs to know.

By playing what is essentially a B Phrygian rather than a B Dominant we can vary the sound of our Alzapuas for Alegrias in E, while also making like just a little bit easier on our left hanD.