How to explain a position?

Hey peeps,

When I'm playing I often find myself in the position.  If black makes a move that doesn't defend the pawn in the centre, I take the knight (sacrificing my bishop) so i can then take the pawn and be a pawn up.

I'm starting to wonder if this is worth it though as if they take my bishop back with the pawn closest to the rook, they the rook can easily be released.  If this has been discussed before please let me know where.

Thanks 

If black plays a6 attacking the bishop and your bishop takes the knight, you cannot take e5 because of Queen d4, attacking both knight and pawn, if he took your bishop with the d pawn. This opening is playable, after your bishop is taken, I would recommend castling, so that the threat on e5 becomes real.

http://en.wikipedia.org/wiki/Ruy_Lopez,_Exchange_Variation