Content Glass web client store multiple type of information locally in the browser's storage in order to improve its performance and make working more efficient. For example HTML template data used to construct views is stored locally. Widgets are stored locally to be available also when off-line. Theme settings and log data are also stored locally. Social networks data is stored locally to prevent from user to login a network again and again.
Sometime you may want to clear this cache. For example if you added new contacts to some social-networks and you find that social-account does not show these contacts (usually refresh is sufficient). Note that clearing the cache will also create new Client-Id so if you involve with chat you may need to identify yourself again and old messages will not be presented to you.
Most of the time you will not have to use it but when you do you can easily clear the cache. All you have to do is to open the main menu and click the "Cache" button. Then confirm the operation and cache will be cleared. The page will be reloaded so that Content Glass wil recreate the basic storage resources again as well as new Client-Id,