The household runs on one person's knowledge. Consider what happens when that person is unavailable — not permanently, just for a week, unexpectedly. Who pays the mortgage, who knows the alarm code, who can reach the insurance company.
The two bad answers
The first is to share everything now: joint access to all accounts, passwords written down, no boundaries. It solves the emergency and creates a permanent privacy problem, and most people quite reasonably will not do it.
The second is to do nothing and assume it will be worked out. It usually is worked out, eventually, at considerable cost and stress, by people who were already having a hard week.
Break-glass is the third answer
The useful shape is access that is granted in advance but only opens under conditions: a trusted person can request it, you are notified, and a countdown runs during which you can deny it. If you are fine, you deny it and nothing happened. If you genuinely cannot respond, the countdown completes and they get in.
That structure gives you the emergency answer without giving up privacy today, which is why it is worth the complexity. The clock skew, the denial race, and the notification path are all genuinely fiddly to get right — but the alternative is one of the two bad answers.