What room, item, or ability did you under-utilize when you played the game?

For example, I never really used the Laundry Room, or thought about it. When it was time to unlocked all the chests at the bottom of the reservoir, I just chipped away at them over time with my spare keys. It wasn’t until much later I realized I could have used my considerable allowance in the Laundry room to give myself plenty of keys.