Precaching data is an option that allows you to load all of the household information of your area into your computer's memory. This can increase the performance when applying different household layers and filters at the expense of a one-time load that occurs when activating the 'Precache data' option. The effects of this option will last through your current browsing session or until you refresh the page.
To precache the data, find the 'Precache data' heading in the 'Options' section of the control panel and click the toggle to the right of it so that it turns green.
Activating the option will cause your map to become grey and a box to open in the center of the screen that details the current status of the load. It may take several seconds for the number to start changing.