I agree the best practice for compiling job descriptions falls between the manager of the position and HR. Generally we also have employees/applicants read over the JD so they understand the position at the time of hire and then later if changes are made.
I will say when I took this position in 2005, we had none. One of my projects was to make sure there was one for each current position and one for whatever position(s) we are currently hiring. By creating them, it helped flesh out the job qualifications, responsibilities, etc. And I love being able to place the JD in front of an applicant, ask them to read through it and acknowledge that they can perform the duties as listed. Then later if they can not, we have a point in which they told us they could to reference back to if needed.
Honestly, my managers don't like doing JDs and are more than happy to let me handle them. I just ask that they review them when needed.