Yeah I think with rumors/information it's part of the investigative mini-game. The reason you wouldn't just tell them that the treasure is at location x is if you think the management of information is part of the point of the game. It's sort of like the quantum ogre but with locations--they can't go to both location x and location y at the same time, and only one of them has the thing they are looking for, and they may run out of time if they make the wrong choice. So they have to piece together the clues they've assembled to make the right choice. I can see a dynamic CoC scenario running like this.What's the difference between (i) the players knowing their PCs are at the dungeon/module/adventure - rather than in a dead end or a place with no treasure etc - and (ii) the players knowing they're at the place in the dungeon/module/adventure where the best treasure is?
I think in some RPGs - I've got in mind MHRP adapted to Cortex+ Heroic Fantasy, and Burning Wheel - to the extent that the question makes sense, the answer is that there's no real difference.
In B/X D&D, I think there's a difference, but it's not about whether or not metagame knowledge is a bad thing. It's about how (i) and (ii) are differently related to the process of play, and how hidden information is a part of that process.
Even if the characters have all the information to make those choices in the fiction, it probably does require some amt of metagame knowledge of game conventions for the player to know how to navigate those scenarios.