There's no real benefit I can think of to porting your Google Voice number to your carrier except one: if you've had GV a long time and most calls are to the GV number so that it's effectively your main number, BUT you're experiencing poor call quality, porting the number to your carrier to improve quality while keeping your most used number makes some sense.
That said, my wife and I have both used Google Voice for years and thousands of calls and never had a problem with quality or reliability. But having 2 phone numbers per phone, basically 1 public and 1 private, plus all the features GV adds and all that for free, has been terrific.
Android since v1.0. Linux user since 2001.