These shampoos are good to use if you use a lot of hair product. Hairsprays, gels, etc., they tend to build-up on hair and normal gentler shampoos don't get it all off your hair. In time, this leads to dull lifeless hair. Every now and then (NOT all the time) it's good to use an anti-residue shampoo to get all the hair goop off your hair. Once or twice a week at most, one would use this type.
The down side of these shampoos, is they can be very drying if used all the time. Also, you are right, it can pull some deposited hair dye out of the hair.
Hope this helps!