First: organization. If I grab a chunk of function and put it in nicely named subfunction, even if it is only called once it lets me keep each function to a nice size. This could be done with a static function, but then you always have to think: "What else in this file might call this function?"

Second: (And much more empowering) Gathering together repetitious code can be cleaner. Consider implementing some network protocol. You will probably have a "get next byte from buffer" function which will need access to the buffer, the current position, the number of valid bytes in the buffer, and who knows what else. You could make this a static function and pass all the arguments in, correctly, each time and if you only need a single value back that works. With a lexically scoped subfunction you can just reference these in the outer scope and if you need to set an error condition or message just set it in the outer. Very clean. No scary runtime code.

By all means play with closures. I don't mean to discourage the original poster from experimenting. I am just pointing out some irony in the context of gcc and clang. Clang is forced to implement nonstandard gcc extensions. I do not see this as a good thing for languages that are essential building blocks and which people have put a lot of work into standardizing. Software development doesn't need to be so ephemeral.