In the Lucas biography "Mythmaker" by John Baxter, the story goes that during the filming of ANH the original ILM guys were a bunch of hippie stoners who would sit around and screw off all day instead of completing the shots they were supposed to be delivering. And the stuff they did manage to deliver was unusable crap. At that point, between various on-set disasters while filming the actors, overseeing the editing of the dailies, and driving to the ILM facility to try to motivate the special-effects team, Lucas was on the verge of a nervous breakdown.

So, I think Coppola suggested Lucas hire this Kazanjian guy to be a hard-ass, no-bullshit, budget-nazi "enforcer", to make sure Rydstrom and the other ILM guys got the job done on schedule. He took up an office at the warehouse Rydstrom and co. were using for a special effects facility, and supervised their daily progress, and when he wanted something, he didn't say "please". Unlike Lucas, he was not a pushover, and for that reason he was resented by the crew. He was almost like the "Darth Vader" of the production. Feared, respected, and hated, Lucas' "sinister agent of evil".

Obviously, the relationship between him and Lucas worked, he got the job done, so Kazanjian was brought on again as a go-between for Lucas and Kershner during the filming of ESB.

He went on to work on Raiders of the Lost Ark and ended up filling Gary Kurtz' position on Jedi. For some reason Lucas and Kurtz had a fall out.

I don't think Kazanjian was brought in for any of the Prequels, but I could be wrong.