I have never had extensions, but some of us are unable to grow long hair. Once my reaches a certain length, it just seems to fizzle out. Also people use it to add more fullness and body to their existing hair.
I just ordered mine . My hair is a little past my shoulder but I want my hair longer. I got them to have get my hair longer. I'm trying to grow my hair out though so I probably will only keep my extensions in until my hair gets to a certain length I am confident with.