If you have been using your Mac for any length of time you probably have a reasonable number of applications installed. OS X can automatically check for the availability of updates for the operating system as well as various Apple applications, and there are a number of programs that will check for updates when they are launched.
However, there are plenty of software titles which do not feature any sort of automatic update facility and this could mean that you are missing out on important feature and security updates.
Obviously, there is nothing to stop you from visiting the web sites of software manufacturers to check for new program versions and updates, but unless you work with a very limited number of applications this is likely to be an incredibly lengthy process.
AppFresh can do all of the hard work for you. The tool integrates with OS X's own update checker and it will check for updates for all of the program you have installed; these can then be installed at your leisure. The program can also update widgets, plugins and preference panes making it a truly essential tool.