By the rules it IS used to detect 'all the things ever!'. Your passive perception is always on and spots all secret passages, hidden items, traps, and hidden creatures within your line of sight all of the time as long as your passive perception is equal to or higher than the DC to spot something.
On a side note, it is interesting that JC decided to spell this out. I've been wondering how they actually felt about PP since I first read the book. It said PP existed and if it exists then it really should be the "floor" of your perception. But allowing it to be the "floor" means that a large number of traps become completely useless. It really changes the feeling of the game when in one game you say "I walk forward" and the DM says "You fall into a pit and take 10 damage" and you say "I climb out and keep walking down the corridor" and the DM says "You fall into another pit and take 10 damage" VS a game where the DM says "Your passive perception of 15 lets you see 5 pit traps within sight, each one is 5 feet by 5 feet. You can see where the edges of the pits are so you can just step around them."
I'm honestly not sure which type of game I like better, but the different rules create very different games.
Listening to JC's podcast and reading his 5E rules, that's not how 'always on' works.
For example, lets say that you (as DM) have set up a room with a cupboard, a chest of drawers, and a hatch door under a carpet. You've put a clue in the chest of drawers, a fancy cloak worth 50gp in the cupboard, and a carpet over the hatch.
For the clue: it's hidden among some papers so you've set the DC at 20.
For the cupboard: spotting the cloak is automatic as soon as you open it, but it's DC 10 to recognise its worth.
For the trapdoor/hatch: automatically spotted if the carpet is taken away.
What happens when the PCs enter the room? One guy has a passive score of 20 so he spots everything just by entering the room? No, that's not how 5E works.
In 5E, you tell the DM what your PC is doing. If no-one moves the carpet, no-one spots the trapdoor. If the carpet is removed than everyone present can see the trapdoor automatically.
If the cupboard is not opened then no-one can see the cloak and its worth is not an issue. If someone opens the cupboard they spot the cloak, and a passive score of 10 or better means that it's obvious it's worth a lot. If the passive score is less than 10 then if the player asks questions about the cloak allow them to roll and if they get 10 or more they realise the cloak's value.
If no-one opens the drawers then the clue
cannot be discovered, no matter what your 'always on' passive score may be. Once a PC opens the drawers and searches them, if they have a passive score of 20 or higher then they spot the clue. If their passive score is less than 20 then let them roll as they search the drawers. If they roll 20 or higher then they spot the clue.
This is how 5E works and is intended to work. DMs need not fear a PC with high passive scores who just turns up and magically knows everything, because that's not how the game works.