How do you guys justify both to yourself and to clients the use of CSS vs. the old way of just using tables?

This is a pretty interesting debate as the CSS purists say it's for standards, clean code, separation of data, etc., but in the end, how can we justify this to our clients?

The most effective argument to make when talking to clients always revolves around money.

Client: Why not use tables?
Web Guy: Tables require more markup which means more bandwidth which costs more money. They also take more time to maintain. More time = more money.

That usually does it because, face it, most clients don't really give a crap if it's CSS, tables or Flash. Just let them know that they will be saving money in the near and long term with a CSS based layout.