It seems there is still some confusion on what Insight exactly does. It has many uses, though it's utility has been tremendously overestimated at launch. There was much speculation, but only the following things are actually affected by Insight (note I am talking about the Insight stat on your hud that ranges from 0 to 99).

0 Insight

• Witch of Hemwick will not spawn Mad Ones during her fight.

1 Insight

• The Plain Doll comes to life, allowing you to level up your character.
• Beckoning Bell and Silencing Blank are received through the Messengers in the Hunter's Dream.

10 Insight

• Insight Bath Messengers shop becomes available.

15 Insight

• Lamp Pimps in Cathedral Ward gain a projectile attack.
• Scythe Pimp in Cathedral Ward gains a weapon buff.
• Cross Pimp in front of the Grand Cathedral gains a small passive AOE frenzy, in addition to a weapon buff.
• Mad Ones (the enemies Witch of Hemwick summons) will spawn in Hemwick Carnal Lane if you have learned the password.
• Gehrman mumbles in his sleep in Hunter's Dream.

30 Insight

• Brain enemies start singing off-key.

40 Insight

• Lesser Amygdala's are visible before you defeat Rom.

50 Insight

• Hunter's Dream music changes before you defeat Rom.

60 Insight

• A crying baby can be heard occasionally.

0-99 Insight

• The higher your Insight, the lower your frenzy resistance will be (resulting in becoming frenzied faster).
• The higher your Insight, the lower your Beasthood will be (resulting in dealing less damage after using Beasthood Pellets or innate Beasthood weapons in relation to if your Insight was lower).

Note: Most visual and ambiance changes occur automatically after defeating Rom and Insight will have no affect on this anymore.

That's all there is. There is some speculation whether or not the enemies in Lecture Hall may gain additional attacks at higher Insight, but it's unproven. Otherwise, much of the other rumors has to do with the fallacy of people assuming Insight is responsible for what happened without actually testing it thoroughly. For instance, the Amalia dialogue that was supposed to happen at high Insight also happens at an Insight of only 2. The difference was the person with high Insight walked slowly towards her and assumed his high Insight was the cause. Instead, you can slowly walk up to her (before she transforms) and the dialogue triggers no matter what Insight you have.

That's not to say this is a definitive list, some stuff might still be undiscovered. But things like damage increases, damage decreases, boss moves/damage and whatnot have been thoroughly tested and debunked.

Sounds like a fairly accurate list to me. People make a big deal out of insight for some reason, it really doesn't do much at all beyond the first 10 points.

Huh, that one with the Witch is odd.

Maybe I'm misremenbering but I thought you could hear the baby everywhere? Or maybe is it just in the nightmare at the end?

But you can hear some stuff right if you stand still and wait? Or am I going crazy...

Thanks for the list, this is interesting to know.

What an underdeveloped system with so much potential.... Shame :(

You can hear the baby in the Mensis Nightmare period.... the rest of the game you only hear the baby at 60+ insight. So yeah at say 70 insight you will hear the baby in Central Yarhnam, but in Mensis you will hear it even at 0 insight. Well at least until you finish the zone anyway.

It is impossible to get to Mensis without killing Rom first. Also I am 100% sure I still don't hear the baby sub 60 insight outside of unseen village and mensis post Rom death. As for witch, you are right, but you can always die, get rid of the point, then go back at 0. To be specific the 60 insight thing is any zone, any point in the game. Like you could start fresh NG+ cycle, be in Odeum Chapel with Amelia still alive not even visited the woods yet and hear the baby crying if you have 60+ insight.

@dudeglove: first encounter grats 1, but if you waste it after you die I think you'll be set to fight with 0

Uh... what? How? I thought the only way was Rom -> Unseen Village -> The One Reborn -> Lecture Hall 2nd Floor -> Nightmare of Mensis

I believe you misread what he said.

Agreed. I thought the 15 Insight cut-off was the start of some amazing play with Insight for the rest of the game, but it just didn't happen. It makes some narrative sense that most changes would occur in Cathedral area's, but still it would have been awesome if other area's had enemies change movesets as well. Or at least more of this stuff. It seems a little bare now.

@he1ixx_gb said:

This is how it was explained to me.

This is the best explanation I have ever seen.

I think they kinda had to make it such an easy resource to get since it's your multiplayer "currency", and that's probably Insight's main purpose too. Humanity did even less than Insight, and it's sad that they didn't do as much with the concept as they could, but it just feels like a cool little touch to a system that was already in place.

I've actually never experienced the speculation period of one of these games before, and it's pretty fun to watch. For me, it's actually more interesting to read about that stuff and get inspired to mess around in the game yourself (even when you know it's pointless), than it is to read a factual list that lays everything out.