To be fair maybe it depends on age/life stage... When I was a younger man in a shared house at University, friends/family could and did just walk in and no one cared.

And that place had dried mashed potato stuck to the ceiling.

My door is always open to friends and family.
They take me as they find me.
I love company.

Bloody hell.

Like I said if it’s truly a surprise-visit then it shouldn’t really matter to them how they find the house/flat in any case (so long as it’s not too bad). But people who aren’t necessarily trying to surprise you but just drop by randomly without even being in the area or thinking to leave ordinary messages are annoying. If one was to be really antisocial you’d just shut the door on them and try not to feel too awkward about it.

I see. I guess when you’re not very social anyway and fond of your own space having people you haven’t specially planned for turning up even with notice can be annoying.

When you’re living with other people/flatmates who you don’t really know or like enough to want to get to know them better people (from students to grown professionals/people otherwise in house-shares) tend to just stay in their rooms when they haven’t got somewhere to be (going back to Soldier Boy’s point), not because it doesn’t feel a little too cagey in there sometimes but because when you give your daily hustle and bustle a bit more of a social touch these annoying near-strangers will always bother you and ask too many questions. It’s not so much the contentment with being a total recluse (people generally cultivate social circles with people they actually know well outside those walls if they’re not trying to get to know the people they happen to live with better or just have boundaries when it comes to personal space) as it is just wanting those space-boundaries to be respected. A lot of extraverts find it hard to do/understand that and think they’re entitled to be your friend just because you live together. Age can help but it doesn’t always and that sense of let-me-in-nice-stranger-I-just-happen-to-share-a-living-space-with definitely carries on at times well into one’s 30s.

No surprise visitors.

It’s all about taking people as they are. Especially if they’re supposed to be close friends.

You mean you don’t clean the whole house, mop it (if it’s that time of the week) and fetch them some tea and biscuit and a bottle of Lambrusco each for the road?