Why use XML?

Hello,
Im interested in learning and using XML and eventually all the
great things that come along with it.. and I even want to ask my
boss to pay for some training in it.. I know what XML does and
its uses but, maybe its just me, I haven't found a clear answer
that i could understand and then tell my boss... but why would
you want to or need to use XML for a website? Hope someone
can clear it up for me thanks!