What does an employer want to see from recommendation letters Assume that one is searching for some permanent research positions. I am a bit curious what does an employer wants to see in recommendations letters.

Obviously, recommendations have nothing to do with scientific achievements. For that, they can check the publication lists. As I can imagine, the purposes of recommendation letters could be:


demonstration that the applicant can socialize normally with other
people
they want to see recommendations from high-profile people, since these  demonstrate that the applicant has established enough connections and potentials for influence in the community
they want to see recommendations from the applicant's current boss, since it demonstrates that the applicant has worked hard and loyally for his/her current employer
they want to see recommendations from people who they want to collaborate with, such that hiring the applicant would help with social connections
(from  xLeitix) they would like to see the community's view about the applicant's work -- which means anyone in the community qualifies as a referee.


Are these valid purposes for recommendation letters, and what else am I missing here?
I think all 5 points are valid. I would add two more:


Due diligence: Institutions want the insurance in case something goes wrong with the faculty in the future, e.g. the person commits scientific fraud or sexual harassment. Of course, there can be nothing in a recommendation letter that would guarantee that the faculty will behave, but in an inquiry, the institution must be able to say they did their due diligence. So, they just need a certain number (typically three) letters on file, not necessarily for their content.
Intangibles: They want to see enthusiasm in the recommendation letter. I have heard many times that a merely good recommendation letter is a terrible recommendation letter. If someone's adviser/colleague cannot be bothered to write superlatives for the candidate, it might be a "red flag" that there might be a something intangibly wrong with the candidate.