They say that so you'll run out fast, and it's unnecessary, unless you haven't showered in weeks.
You should invest some shampoo and conditioner at LUSH
I know there's a really good conditioner to help damaged hair and it's sulfate-free. Sulfate-free shampoos don't damage your hair like regular shampoos. Sulfate is the chemical in the regular shampoos like TreSemme, Pantene, and all that jazz that dries out your hair even thought it feels like it's conditioning it in the shower.
The conditioner I recommend for use is called RETREAD from LUSH and it comes in a black pot. If your hair is damaged this one will get it right back on track, trust me.
Also, if you'd like a natural shampoo, try TRICHOMANIA It has coconut shavings and natural ingredients and is in the form of a soap bar.
I started using LUSH because it's natural and I've seen really great improvement in my hair,
ALSO WHEN YOU USE RETREAD IN THE SHOWER, It may not feel like it's doing anything but really it's conditioning it even if it doesn't seem like it, it's because it's sulfate-free.
Anyways, good luck! :)
Using mayonaise and/or olive oil & eggyolk treatment for your hair will work to moisturize it if it's dry!