Is it worth mentioning money figures in a job interview?

In an interview setting, the employer may ask if you have in mind a salary expectation. At that point, you're probably wondering whether or not you should mention a figure or leave it up to them to mention what's on offer.

It's a hard call to make because on one hand, you want to be paid what you're worth, but on the other hand, you don't want to miss out on a job because you mentioned a figure that was way off what is being offered.

This is a personal decision to make. The question is, whether it's 'worth' mentioning money figures in a job interview. I think that if you are asked what you're expecting, it's important to be clear as to what you think you are worth, while being realistic about it all and then if you want, mentioning why you think you are worth that amount.