Now everyone except experienced players thinks that Coroner is really useless since the Coroner only shows what role did visit the dead target and whom did the target visit. Which if the target is Town; they'd 90% put ther lwes who did he visit. Cause of that reason the unexperienced players thinks coroner is useless.
The Thing that they don't know about is fake claims. Fake claims are the savior of the non-town roles. Non-town roles such as Mafia, Triad, Neutral Evil/Benign/Killing can claim easy roles such as Doctor, Bodyguard, Sheriff, Detective, Jailor (if Kidnapper or Interrogator is in-game), Escort (if Consort or Liason is in-game). Now that's where coroner starts so be so useful. Let's say our little Serial Killer made a claim about being Doctor and said his lw is : N1-5 N2-1 N3-2... Now let's assume 1 died N3 by Mafia. And Coroner checked 1 and didn't see any doctor visit him. If Marshall or Mayor trusts the Coroner which none of the evil roles claim that role since it's too stupid and long lwed role, Marshall or Mayor might be aware of that and lynch the SK at D4. This is mostly why experienced players say Coroner is useful but that's not all.
Now let's say Godfather and his teammate Consort backing up each other. Consort says; I rbed Godfather N2 he wasn't immune.
Then everyone will think that Godfather isn't actually Godfather since they trust Consort aka fake Escort. But let's assume Godfather died to Veteran and they saw he was Godfather and town didn't actually care about Consort's lie.
Now that's where Coroner makes his move, he very well knows Consort is a pretty much liar and he actually backed up Godfather, and since he has no real proof the Townies wont believe him. He goes to him and sees he wasn't visited by anyone at N2. Now he actually has a real proof about "HE IS MAFIA"
and because of that he can actually courage town to lynch former Consort new Mafioso. And that's why Coroner is useful.
But yes the Coroners are most usefull at Janitor or Cultist games but that doesn't make them useless role at normal 9-3-3 games.