htaccess for URL remapping, caching, and compression
Leverage browser caching is designed to prevent browsers from using a cache for too long. If your website is dynamic, this is necessary to prevent users' browsers from storing your website for too long.

The way your file does this is by checking the type of file, and making a browser's cache of it expire after a specified amount of time. Images the other files you listed generally change little, so that part of you code is good unless you create dynamic images often. Your XML and TXT file deadline is okay unless you have XML news feeds or similar. HTML expiration date is also good as those files are usually the most often edited.

Overall, your file structure is good. I am sorry if this did not answer your question.

Edit:
Note that a browser doesn't have to obey you request to revalidate the page.