There are lots of reasons as to why you should become efficient and diligent when it comes to properly cataloguing your files. If your images have proper keywords and captions, it becomes a lot easier to find them at a later date, when you have a large library. Finding files in your library is only one example of why metadata is important and keywords and captions are just some of the information that you can embed.
For example, if you use a stock photography service to sell your photography, having proper metadata will be a requirement of that service, and it aids you in selling your images. Because most search engines can't understand visual data, you need to be as descriptive as possible. Many services also have rules about what other information you need to add. Even if you are just posting images to your own website, it is important that you have copyright information and contact details embedded in your images. If you shoot sports or press photography...