The only bridge across the reset
Most items reset with the manor each night. The Coat Check room is one of the few ways to hold an item past the daily wipe, letting you bank a tool you are not ready to use yet.
When it earns its door
Use Coat Check when you find an item that clearly solves a later puzzle but has no use in today’s route. Storing it keeps it from vanishing, so the day you need it, it is waiting.
What to store
Bank items that are specific and hard to re-find: a key for a wing you have not reached, or a tool tied to a clue you have not solved. Common filler is not worth the door.
Planning around it
If your route depends on a stored item, draft Coat Check early and know which room you will pull it from later. The item database is where you confirm what an item actually does before you commit a slot to it.