If you have some thing(Properties or functions) to call from the normal page to master page you normally call using type conversion or if you want to call some controls on the master page you achieve with FindControl method.

If you specify mastertype of the page level you can strongly call the functions and properites on the master page just refering Page.MasterPage method .with Visual studios intellisense support.

<% MasterType VirtualPath="MasterPage.master" %>

Isnt it good practice, also you can find most of the errors at compile time rather thatn at runtime.