Brett Cannon added the comment:
I know it has it's uses (avoiding stat calls is one of them), but it is still undocumented, untested, and has two comments in it saying it needs work. Because of all that it might as well not exist since it doesn't meet our standards of quality.
If someone wants to fix all those issues then we can properly document it as supported, but if no one is willing to then I don't think we should leave unsupported code lying around that people might discover through dir().
And it doesn't serve a _different_ purpose compared to resolve(), it serves a _subset_ of resolve()'s purpose since resolve() calls absolute() unconditionally.