[asveikau]

Maybe first ask yourself why have a MAC address at all, then the answer will come to you.

I find it interesting how many people will stumble over this concept. A lot of technically minded people know that a MAC address is a "unique identifier" for the network card. They have that phrase "unique identifier" fixed in their heads and they know that MACs are this. Pull out a question like "why would you want a unique identifier?" and you get a lot of blank looks. It's almost like it's too easy to latch onto a phrase like "unique identifier" and get distracted from its practical purpose. (That thing that tells you whose packet this is.)