As a student before mobile phones, we all did it, all the time at random times of day and night....and I loved it.
As an early 20s with a big group of friends, it was fairly common too.
Doesn't happen so much now, because often close friends aren't in walking distance. When it does happen, my house is invariably a mess, which I'd rather it wasn't, but this doesn't make me wish those people hadn't popped by...it usually is a quick cup of tea.....most people don't arrive impromptu expecting more.
I've noticed that where my inlaws live, people are dropping into theirs all the time. They have lots of friends and are retired....busy, but with plenty of time....involved in lots of things and know lots of people and hugely sociable and gracious, so that those appearing feel welcome, even if it is a bit inconvenient. And they are laid back and recognise that most things can wait a bit and people are actaually important.
I think a lot of our attitudes towards this kind of thing comes down to whether we are gracious people or not.....whether we are willing to put others first and make them feel at ease, even if it's a a bit inconvenient. I don't think I'm as gracious as my inlaws, but I'd like to become more open and welcoming like them to be honest.