I never used the objective line until I had to retool 15 years of library experience into a resume for tech writing/editing. Basically, I've all but given up finding library work after an agency-wide layoff (and the public libraries are laying off librarians as well, so no work there, either) and have rewritten my resume to show off my non-library skills.
The reason I'm using it it to answer the question "If she's been a librarian for the last decade, why does she want this writing job?". I'm assuming private industry HR may not be following the budget news for state and local governments to the point where they know that library work is scare in this county right now, so they may not understand why I want this job that I can do, even if I haven't held a job with that specific title.
But I agree that if your resume has reference librarian all over it and you're applying for head of reference or branch manager, citing your objective is redundant. Which is why I never used it before.
for the curious, mine says:
OBJECTIVE: Obtaining a professional position that takes advantage of my extensive research, editing, and writing background and in-depth computer skills.
and then goes on to describe said skills in bullet points. next comes work experience, and then education is at the bottom, since it's doubtful any of the companies I'm applying with will care that I have an MLIS (whereas it's the first thing on my library-specific resume).
Does this seem logical? I suppose instead I could put some kind of summary line on top that boils down to "Ex-librarian has research, editing, and writing skills and could totally do this job of writing your employee newsletter and corporate communications if you'd just look at my skills section and not so much at my past job titles", but it seems like that might be less useful. I don't want my resume to scream "I'm changing careers because there is literally nothing left to apply for in my field unless I relocate" even though that's more or less the truth.