There are a number of ways you can, or cannot, use titles in your slide. See the examples below. (RSS subscribers might have to open the post on the web to see images).

The classic way is a basic description of what the chart is showing.

The management consulting approach is the message title: write out in a sentence what the chart is supposed to say, and put the description and unit of the data in a subtitle

You can spice things up with an image

And with full image slides, the traditional title does not actually really matter anymore. You can place text anywhere on the image to get your point across. If you are presenting live, you can even omit the exact description of what you are showing