The advantage of "everything-is-a-file" is that every process gains thread-safe access to some API without having to pull in the headers, link, and manage a foreign memory management regimen.
But the real boon is that each process can conceivably be linked with any 'file'. I liken this practice to the STL library's iterator pattern: algorithms are the processes, and files are the iterators (although I bet STL was inspired by unix). You can redirect your tty through an ssh tunnel, you can scp a regular file, or you can ssh tunnel your soundcard or mouse. And of course 'ssh tunnel' is only one such kind of glue. There are pipes, devices, fifos, etc. In the end it works out that there are O(n*m) possibilities for only O(n+m) implementation cost.
But remember that with STL, not all algorithms will work with all iterators, and vice versa. And likewise, not all processes can work with all files, and vice versa. The benefit comes from the significant overlapping portion.
But the real boon is that each process can conceivably be linked with any 'file'. I liken this practice to the STL library's iterator pattern: algorithms are the processes, and files are the iterators (although I bet STL was inspired by unix). You can redirect your tty through an ssh tunnel, you can scp a regular file, or you can ssh tunnel your soundcard or mouse. And of course 'ssh tunnel' is only one such kind of glue. There are pipes, devices, fifos, etc. In the end it works out that there are O(n*m) possibilities for only O(n+m) implementation cost.
But remember that with STL, not all algorithms will work with all iterators, and vice versa. And likewise, not all processes can work with all files, and vice versa. The benefit comes from the significant overlapping portion.