-key purchases
-location of items that only town would want (like doctor, or cop). to some extent also tracker/watch-like roles
-valuable investigative info (getting a scum result on a player)
-location of platinum, poorhouse, garden, or unknown rooms, unless you are in this room.
So these are the four things I think should be claimed. Key purchases help town in these ways:
-town knows that they can enter a room for a cheaper cost
-if the claimer is scum and someone enters that type room at the normal price then scum is caught.
-if claimer is town and someone enters a room at the cheaper cost then the claimer is IC.
-unknown?
helps scum:
-knows town can enter those rooms for cheaper.
-knows player X bought key, and so likely doesn't have much else (at least at this early stage)
-unknown?
I don't THINK scum killing a player who bought a key takes away the bonus from the rest of the faction. this is from the OP, where it says "Cost to enter a gold room: 5$, 2$ if gold key purchase by your faction" which seems to suggest that it just matters that is has been purchased. I PMed robz to make sure.
I feel like here the things that help town outweigh the things that help scum, because making ICs and catching scum is very very powerful. Yes, it is possible that there is an unknown that makes it a bad idea, but I believe it is worth the risk.
I'm not so sure about the claiming locations of items that town would want more than scum anymore. This is because, if you know where such an item is, then you are likely very nearby and should just buy it yourself.
valuable investigative info: this one is obvious. If you got a cop item and found scum, of course you should claim that at some point in the day. Same is true for anything similar to that.
About claiming the location of rooms: this is probably only a good idea if you aren't going to be entering that room. In general, the location of a room being public info is good, because there are more town than scum, and so town will more likely be able to get there first. There is also a good chance that all four scum already know where the room is because if just one of them was adjacent to it then they all saw it. However, it isn't a good idea to say "hey guys, there's a silver room in the upper-left corner!" because that gives away that you are in the upper left corner. That's why I only think it is a good idea to claim where a room is if it is a very good room and one that you won't be buying anything from. This doesn't take into account the unknown items, but like I said, it is also possible that the unknown makes it an even better idea to claim some things.