Staff make mistakes and guests at times do stupid things.

I've seen this one a few times over the years. Housekeeping after they're done, will sometimes mistakenly leave the connecting doors open or unlocked between two connecting rooms. Guest #1 checks in to room A and for whatever reason, decides to move to room B while saying nothing yet, the latch and deadbolt in room A are left engaged.

This sets up one of two scenarios where security/maintenance/the GM/the police may need to access the room in a non-traditional manor. 1. The desk thinks room B is vacant ready and the guest they properly check in to room B will likely be locked out with the deadbolt and security latch engaged in a supposedly unoccupied vacant ready room. 2. Assuming the room switch isn't figured out, the next day, housekeeping can't get into room A to check if it's vacant or if the guest has left because the deadbolt and latch are still engaged which still makes room B actually vacant dirty even though the hotel will think the room is actually vacant ready.

Presume/assume nothing because mix-ups and/or odd situations do happen.