Why should I use memcached?
Memcached reduces page load time, giving your user a faster, better experience. Remember, speed is a feature. Without memcached, each page load will need to perform database queries and HTML rendering over and over again. Often these operations take several hundred milliseconds, but sometimes they can take seconds depending on complexity and server load.
Memcached queries return in milliseconds, which is usually 100x faster than a database query or a complex render (again, depending on load and complexity). This allows any database queries or renders that are common to some of your users to be shared. Even operations unique to a user can be useful to cache if the same result will be displayed to them on every page.