What are Expiry dates?
Expiry dates are dates that you can set to let browsers know how long that they can/should cache (store) a file for. This is helpful because when a visitor comes back to a page on your site then the file/resource don’t have to be downloaded again. This decreases the number of requests that have to be made to the server and thus increases the speed at which your site is displayed. It can be very useful to set expiry dates on items like your favicon, logo, and other files that are not likely to change very often.