Hi,
Because the mixolydian scale includes a dominant 7th note; it works well when playing certain blues-rock progressions.
Using the key of C as a reference; here's one example:
I(C) - Dom7(Bb) - IV(F)
-5--------3---------x-----
-5--------3---------7-----
-6--------4---------7-----
-7--------5---------7-----
-7--------5---------5-----
-5--------3---------x-----
http://guitartricks.com/lesson.php?input=13579
Hope this helps you.
Doug
