The added specificity would imply there is more than one form element in the document, or at least provision for there to be more than one, such as a plug-in.
The class name could differ between multiple forms. The part of the selector that doesn't really add value is the type.
form.form => 0 0 1 1
.form => 0 0 1 0
If there are elements of other types that also share the class,
.form they will not be affected by the top selector. Of course the least specific selector is,
form => 0 0 0 1
When writing selectors, create very general rules for type selectors since they will apply across the board. One objective to keep in mind is minimum specificity overall. It is a design concept that takes a lot of practice to learn, but in the long run easier to maintain.
Lower specificity makes it easier to adapt new components in the future.