Depends on the company. Larger organizations will often have a mandate that EVERY hire go through proscribed HR processes and channels. MAYBE if you know a C level person you can get an exception.
Having a friend on the inside avoids two potential filter failures without having to actually change the HR process - it's saving HR the cost and hassle of a recruiter and essentially assuring them that they're not going to get flack for wasting anyone's time if they forward your resume through to the actual hiring manager.