Simply collecting data and storing it on a hard disk is the process that we most commonly follow. But, the problem arises when we wish to retrieve the stored data some time in the future. For example, if we store camera photos in a single directory or upload them to Google Picasa or some other photo site, it will organize them by date.
Many years later, it becomes difficult to retrieve photos imply by scanning through them. Hence tagging them or storing them by the year or by event name becomes important.
Organizing data is a very difficult task and needs dedication. But it pays rich dividends in the end as the data volume increases.
For example, if for your photo collection, you store all files in one directory, the directory becomes too large. Also, you will not be able to locate picture as most of them will not have sufficient information in their tags.