On the study of univalent functions

Question

I am reading one pdf on univalent (analytic + injective) functions. After the introductory part, they said we will study class of such functions on unit disc(${z\in \mathbb C / \mid z \mid<1}$) with normalising conditions $f(0)=0 $ and $f'(0)=1$. Then they gave some transformations which preserve this class of functions. But no reason or any further motive is mentioned why are we focusing on such class of functions. I would like to know that. Thanks.