I work for the company, and the official line is 'To help wash the conditioners out to prevent build up'
Which is, to my mind, utter nonsense.

They recenetly released a 'gentle' shampoo for people with dry or coloured hair, but the only difference is they've subsituted ALS for the usual SLS - it's still sulfites, people!

I find it so frustrating that so few of their products are GC freindly!