It's very rude, it means they believe their time is more important than yours, and you should stop everything you are doing for them.
It might be fine if you are not working or retired and you enjoy visitors.
When people have a job, a family, and are trying to juggle things, it's very inconvenient! Most weekends we are either away, or have friends around, so even if we are not doing much, it would be awkward to barge in!
I don't even answer the door when I am working from home, I have things to do by a certain time, I have planned my day, I don't have time to entertain people.
Even if I am home with the kids, it might be the only evening that week we are home, and we have a school project to finish.
I don't mind if my kids turn up with a friend though, IF they are sure we are around and I don't have to taxi one of their siblings around.
At least my house is as visitor ready as it will ever be because I hate mess, but I still don't open the door if the kids are not around!