Regular cleaning of your makeup brushes will help your brushes last longer and prevent pimples. Dirty brushes can clog pores and provide a breeding ground for bacteria -- something you don't want near your face.
I have purchased MAC's Brush Cleanser ($12.00 for 7.9 oz.) a few times. The one thing that it is missing is a spray cap. Personally, when I clean my brushes I tend to pour out to much (wasting alot). I only clean my smaller brushes (eyes and lip brushes) with the MAC Brush Cleanser. I use Johnson's Baby Shampoo for the bigger brushes (facial brushes). This is my normal routine for cleaning my brushes. Once a month I will do a deep clean of all my brushes with Johnson's Baby Shampoo. Overall I think that MAC's Brush Cleanser is worth the money. It doesnt have a strong scent like some other products that are out there. When the scent is strong you tend to feel the need to rinse them after. With MAC's Brush Cleanser I dont feel that way. I clean them and put them away (without a rinse).