What does it mean if a professor asks you to draft his reference letter for you? This question is, honestly speaking, probably somewhat opinion-based, but I still want to give a shot.

A professor acceded to my invitation of writing a reference letter for me. Nevertheless, unlike the other professors who also acceded to write a reference letter for me, he asked me to draft it on my own. Originally I did not feel anything "wrong", and I just felt embarrassed to recommend myself. But yesterday a friend told me that a professor would ask you to write her reference letter for you when she does not actually think that you are "worthy" enough for her to write you one on her own. 

What is the probability that such viewpoint is true? Any opinion is greatly appreciated!
For me, it means two things:


I am really busy
I don't know anything about the job you're applying to and what you want to emphasize about yourself


If the first draft you write is something I can't sign, I'll edit it or I won't sign it. If it's not braggy enough, I might add some emphasis. But metaphorically handing me a piece of blank paper and asking me to recommend you is actually asking me to put in quite a lot of work. Do these people you're applying to value initiative? Creativity? Willingness to work long hard hours? Cheerfullness? A driven nature? A gentle spirit? Is the fact you write great software relevant to them? How about your careful bench work? For all I know you want to do less of one thing and more of another. So now I need to ask you a zillion questions about what you want to emphasize, and maybe go research the job too, and then ask you if what I've written is ok - frankly, it's way easier to ask you to write the first draft. And some days, I take the easy route.

It does not mean:


I intend to sign words I didn't write. I will write the final draft
It's ok for you to make up strengths you don't have
You'll know what I send in the end
I can't write a simple letter without help from a student.


Your first draft doesn't even have to be a letter, it can be point form. But tell me you're choosing me as a reference so I can confirm your amazing Xness, Yabilty and Zation. If I can, I will.

By the way, I wish I could find the idiot who started the theory that it means I don't think well of you and want you to retract your request. Several students have retracted their requests after I asked for a first draft, and that's a shame, because I would have cheerfully signed a glowing recommendation for them. I just didn't have time to write it all from scratch myself.