Depends. In a perfect world it doesn't matter. However in this imperfect world it is nice to know that there is an automatic backup of your files from a few days ago, and if a hard drive crashes you just replace it (requires paying for redundant hard drives!). The ability to add more space to an existing filesystem is nice just in case.

There are a lot of other features that might or might not matter to you. If the above don't it is because you haven't been burned yet in life. (Or you use one of several other filesystems that support those features)