Especially with the file actually changing names, I cannot recommend strongly enough that when you update Movable Type, you also update your configuration file. Almost every release introduces new configuration directives. If you don’t update your file, you’re going to be missing something – and you may actually run into problems.
Every time I perform an update, I also update the config file. Using a tool like Beyond Compare makes it easy. Just pull up the files in a two-paned viewer, copy your changes in, and you’re done. It’s just not worth the headache of not doing it.
In most cases, you don’t have to update the file. But from one version to the next you will at a minimum see new configuration directives introduced, and you often will see older ones deprecated or removed entirely. In some releases, the configuration file may actually be renamed, so if you go about ignoring the file from one release to the next, you’re just asking for trouble.
Get in the habit of checking the contents of the file as you upgrade, so that you can be familiar with what is inside. That way you won’t be surprised when something comes along, or be sideswiped with a surprise somewhere down the road while others won’t know what hit them. Trust me on this one.