Titles are mostly useful when you need to refer to a photo in a textual form, e.g. on these forums. Saying "I like the 3rd photo in your gallery" is tad ambiguous, whereas saying "I like your 'Beach sunset' photo." is a more readily communicative. While you could refer back to the DSC_42322.jpg name, it's not as descriptive, nor memorable as a title.
So, yes, a title is quite useful when you don't have the original image available to display and want to refer to it in a medium that is not visual.
A prime example is the prat "Prince", or the "artist formerly known as Prince."
As to whether they add to the visual representation of a photo, not really. But what I find very interesting is a description about where the place is, how it was found, what was the event, etc. This helps to set the photo in a context.