If you don't have access to a friendly file manager from your hosting provider, you absolutely HAVE TO HAVE eXtplorer because it lets you manage the underlying files to your site, right from within the Joomla administrator's page. Even if you do have file management access from your hosting control panel, you still can absolutely use eXtplorer, because it so convenient, and it lets you do just about anything that you need to do to files on your server. You can upload, download, edit, rename, change permissions, compress and uncompress files. And you don't have to log into the hosting control panel to do this. Just do it from within Joomla's admin page. You don't have to be a Linux geek to do anything to the files. It's all intuitive, point-and-click. Convenience and simplicity combined! I think that this is a must have extension.
It's so good, that my only concern is that if someone ever hacked into my admin account, they could use eXtplorer do anything to any of the files on my server. (But then again, if they hacked into my admin account, I'm already in trouble anyway.) So a good practice is to zip your Web directory regularly, and download the zip file to your own system. Of course you can use eXtplorer to do this with just a few clicks.
The developers of this tool have kept it free to download - even after continuing to toil over additional improvements and functionality. My hat's off to this group, and I will join their new club, so that I can get early access to whatever else they're cooking up.