What are the pros and cons of using VPLS instead of MPLS alone? What are the typical cases where VPLS is used?
You really can't compare the pros and cons. These are different (but related) technologies and they have been developed for a particular problem. You might as well ask what are the pros and cons of using a hammer vs. a drill.
VPLS can be used when you want to extend your layer-2 topology over multiple sites.