Unnecessary curly braces in C++?

It's sometimes nice since it gives you a new scope, where you can more "cleanly" declare new (automatic) variables.

In C++ this is maybe not so important since you can introduce new variables anywhere, but perhaps the habit is from C, where you could not do this until C99. :)

Since C++ has destructors, it can also be handy to have resources (files, mutexes, or whatever) automatically released as the scope exits, which can make things cleaner. This means you can hold on to some shared resource for a shorter duration than you would if you grabbed it at the start of the method.

One possible purpose is to control variable scope. And since variables with automatic storage are destroyed when they go out of scope, this can also enable a destructor to be called earlier than it otherwise would.