Conclusion & More Information
Of course, I can't list every possible use of htaccess here, just the more notable and useful ones (read: for fun and profit). There is a list of Apache Directives you can use for your htaccess files, though not all of them are designed to be used by htaccess. Consult the documentation for the directive you are looking to use and make sure that you can actually use it as an htaccess string.
You should also go through the Apache User's Guide for more detailed information if you are really serious about making your life easier as a webmaster. You don't need to update all 4,000 of the pages on your site individually, by hand, in order to change one file reference...honestly!
In any event, I hope you got a better idea of the power available to you through this relatively simple little Clark Kent-ish file. You really do have the ability to save yourself a lot of time and grief by using htaccess, especially when you add to that the power of SSI and xSSI.