Edit: When I first wrote this post,
wysiwyg api module was not quite production ready. Since then, a lot of work has gone into that module and that is what I now use and recommend to anyone. It will allow you to use either TinyMCE, FCKEditor, or many other editors. My favorite is actually TinyMCE
With the web being the interactive place that it is today, there is no doubt that most sites need an easy way for users to express themselves. Since a large marjority of communication on the web is done with text, then the more control you have over that text, the more expressive you're able to be. In days gone by, the only choice was to hand code HTML tags. While this still works, only a very small percentage of people understand how this is done.