The most humorous implication of not policing player knowledge is a party who never speaks to each other. The player speaks, and other characters think they know what that character is thinking. It's permanent Telepathic Bond.
For example. A rogue is scouting dark tunnels, and the rest of the party is getting live updates on what the rogue sees. Or the wizard gets mugged while shopping, and the party across town come running.
Granted, this absolutely would make the game run faster. I won't deny that for a second.
Not really a problem. The players come up with in-character reasons for why they perform certain actions, and I, as GM, adjudicate them. I already don't take the rogue aside when scouting alone so all the players see the play already. Hasn't once been a problem, because I'm not super keen making players wait around until enough time has passed or one thinks of an excellent enough justification to go help the rogue. I'd rather everyone be engaged in the game, and the players will almost always solve this problem for me by stating a rational.
Look, ultimately this is on the GM, again. If you're running a game where 1) a rogue scouting alone down dark and distance tunnels is a smart play and 2) you're going to reveal details to the rogue that will impact whoever follows after without them seeing it as well, then you've set up your own problems. Usually, I'll completely elide a moment by moment scouting mission like this, and ask for a skill check to determine what happens, then narrate the entire scout. "Okay, Bob, your rogue (also Bob) is going scouting. How far are you going and what are you doing? " "Um, I'll head out about 15 minutes scout ahead, keeping quiet and being alert for bad guys, I guess." "Cool, give me a DEX check to remain quiet. DC 15 as this seems a medium challenge." "I'm gonna use my Stealth proficiency <clatter> 12?" "Okay, you move ahead, and shortly find that the passage opens into a large room. Smoky fires near the far wall illuminate the room and you see shadowy figures moving behind them. They look armored, medium sized, and humanoid. There's maybe 12 of them, total. You're pretty sure that if you approach more closely, you'll be spotted, though -- the entrance to the room is as far as you can go on that 12. What do you do?"
This approach -- check using success with cost or limited success. Bob gets some info, and is told this is as much as they'll get. They can return to the party and tell them, or do something else, but the party can then decide, perfectly in character, that Bob's likely gotten into trouble (I mean, if Bob tries something else, this is a perfectly reasonable assumption about Bob) and come investigate themselves.