Sacrificing A Piece of More Value for Less for Positional Advantage

I've noticed that in playing some higher ranked players they will sacrifice a piece of more value for a lesser one for positional advantage, this can really throw people off.  I thought I would try it out and it did throw my opponent.  Why is he hanging a bishop?  Why is he hanging a rook?  There are plenty of reasons but two sacrifices I don't think are wise.  It means that my first sacrifice was not worth it.  I'm pretty confident on my skills at the moment and I made some mistakes but I'm learning from them.  Constructive criticism is appreciated.  Thx.