noReset just clears the app data, such as its cache.
fullRest uninstalls the app. fullReset is generally used when you have newer versions of the app coming in fairly quickly. So with fullReset, you will always uninstall the app and then automatically install the new version.
Link with details on noReset & fullReset - https://github.com/appium/appium/blob/master/docs/en/writing-running-appium/caps.md