New immigration rules are created by the government all the time. In fact, immigration is an area of law where there are often new developments. Because of the ongoing changes and developments and the creation of new immigration rules, it is important to ensure that you receive up to date information.
Also, if you are making the application yourself, it is essential to keep personally up to fate with new immigration rules and ensure that you are not hindering your application by missing out on the information in the new immigration rules.
The UK Border Agency publishes all new immigration rules on its website, so there is no excuse to be referring to out of date rules.