What does using conditioner first and shampoo last do to your hair?

I use conditioner first sometimes, but I let it sit for a little while on my hair. It keeps the conditioner from weighing down your hair and making it look greasy. I'd recommend it if you have oily hair; if you have dry hair, shampoo first.

As opposed to using shampoo first, and conditioner last, absolutely nothing.

It would defeat the purpose of the conditioner. You shampoo first to clean your hair and then you condition to restore the moisture. Conditioning first and shampooing after would wash out all of the conditioner leaving your hair dry and static-y.

It doesn't really do anything major to your hair, although it's basically just like you're not even using conditioner because your shampoo washes it all out and also dries out your ends. You use conditioner to moisturize your ends, but washing it out just dries them out again.