If you use a Windows machine, you may have got used to the fact that "MyWebPage.html" refer to the same file as "mywebpage.html". This is not the case with all operating systems. For example, Unix-based systems like Linux and FreeBSD consider them to be two different files.

This affects webmasters in a few ways: If Website Designers web host uses a case-sensitive file system and you indiscriminately refer to your files using whatever capitalization (case) you wish, you will find that some of your links will point nowhere.

Even if your web host uses Windows for its web server, who's to say that you won't move to a different web host in some distant future, one that uses a different operating system? If you find yourself in such a situation, going through all your files with a fine tooth comb to fix all your links is not an enviable task.

Perhaps you think that you'll be careful to always refer to the file using the correct case. That's what you think now. But a few years down the road, will you remember what the case is? You may link to that file with yet another new case combination. And when you test the link, it will work fine if your site is still hosted on a Windows server, so you may not know that you have created a link that will potentially break in the future.

Do you really think that others referring to your site will use your case system? Remember that your site does not exist in a vacuum. Others will link to your site, or talk about it in the web forums. Will they bother to learn a complicated mixed-case system so that they can refer to the page with accuracy?

If your page gets linked to from either your site or other sites using different case combinations, search engines will treat each combination as a distinct page. You will run into the duplicate content problem that I mentioned in my article on How to Create a Search Engine Friendly Website.

The simplest way to avoid all these problems is to just stick to using small letters (lowercase) in your filenames.