What is the purpose of letter of recommendation? I have completed 2.5 postdocs in the US. In all of my applications plus a Green Card application, letters of recommendation were a great deal. In all cases (overall, about 10 letters signed by professors at top US universities), I was asked to write the draft and my supporter did not change more than a sentence or two.

I wonder if anyone really reads the letters of recommendation. And if yes, the judgment is simply based on my words about myself.

My interest in the answer is that I am applying for Assistant Professor position now, and my references asked me to prepare the draft. In the past, I thought that it was because of a special trust in me and I wrote the letters with modesty to respect their trusts. Now, I found it is the norm and professors/PIs do not have time to write such letters (there are about 20 postdocs in my current lab). How should I write the drafts of three different letters of recommendations for myself (sounds funny)!
I hate that this is a legitimate question, but it is. Yes, letters are weighted heavily, in my experience. The fact that you (and many others) are often asked to write their own letters is very troubling. For one thing, it's biased. Secondly, confidentiality is absolutely violated despite most such letters being assumed as such. Now you are in the awkward position to have to write 3, and feign separate ghost writers. 

It is impossible to defend this from any logical or ethical standpoint, particularly if confidentiality is assumed. 

The best course of action is to thoughtfully ask the recommender to write his/her own letter. But you can make it easy on them by providing a CV, papers, manuscripts, etc. Give them the information you'd like to highlight but not the words.