Hmmm.... I dug a bit deeper:

In C this practice seems a continuation of an old convention. It was once required by the compiler when returning expressions:

• https://stackoverflow.com/questions/161879/parenthesis-surrounding-return-values-in-c
• https://www.bell-labs.com/usr/dmr/www/cman.pdf#page=14

However, in C++ there is subtle yet very significant differences:

• https://stackoverflow.com/questions/4762662/are-parentheses-around-the-result-significant-in-a-return-statement/25615981#25615981

Well, why not? :)
It's just a question of taste, nothing more.

Why the redundant extra parentheses in the return?