Sulfates in shampoo are bad because they are known to dry out hair when used frequently. Using shampoos that contain sulfates can lead to dryness, irritation and breakage.
Sulfate shampoos don't need to be completely eliminated from a person's hair care routine if one is currently being used and its performance is satisfactory. Since sulfates are meant to remove buildup, sometimes sulfate shampoos can be useful; however, their usage should be limited to prevent any dryness, irritation or buildup. If the performance of a sulfate shampoo is unsatisfactory, then switch to a sulfate-free shampoo; this will still remove any buildup but will be milder.