By 
(This is the CliffsNotes version of Andy’s reply in a forum thread on RocketTheme’s website, which you can read in full here.)
Andy explains these settings in much more detail in the forum thread I just mentioned above, and these are our recommendations for these settings based on his explanations. You can also read more about the Gantry Framework at it’s home on the web at www.gantry-framework.org.
Joomla Settings
Global Configuration » Server » Cache Settings: When you’re finished building your website, set Cache to “Yes,” and Cache Time to somewhere around 30 minutes, depending on your site’s content and how often it changes.
Global Configuration » System » GZIP Page Compression: Usually set to “Yes,” but check it for yourself after turning it on.
Plugin Manager » System – Cache: This handles “page caching,” and you’re better off leaving this Disabled.
Gantry Settings
These settings are found in Extensions » Template Manager » [Your Template] » Parameters » Advanced. When you open your template to make changes to these parameters, the top parameter tells you which version of Gantry you’re using and if there’s a newer version available. In my experience, I usually let the newest version stabilize for a short time before installing, as there have been times that Gantry parameters just started acting weird after an update. I’ve kept some of the previous versions, so it’s not difficult to roll back to an older, stable version. You can also find them at the Gantry archives on Google Code.
Gantry Cache: Turn it “Off” for development and “On” when your site goes “Live.” The Gantry cache is flushed whenever you Save or Apply your template settings.
Gantry GZipper: This compresses CSS and JavaScript files related to Gantry. You should probably use this, but maybe not, depending on your site’s particular configuration. Also, if you decide to use the System – RokGZipper plugin (see below), be sure to turn this off.
Extension Settings
These settings are found in Extensions » Plugin Manager.
System – RokGantry Cache: This plugin flushes the Gantry cache if you make a change in Joomla that is going to affect Gantry. If it’s installed on your site, go ahead and set it to “Enable.”
System – RokGZipper: This is the Big Brother version of the Gantry GZipper, and if you turn this plugin on make sure you turn off the GZipper. This plugin attempts to compress whatever CSS and JavaScript it can find, more or less, which could be good or bad. We’ve had conflicts between this plugin and some third-party extensions, so we generally leave this one off.
Note: If you use Akeeba Backup to backup your Joomla site, and you really should, then you’re going to want to leave System – RokGZipper turned off, as they are not compatible according to this post on RocketTheme’s forums.