Relatives and true friends are always welcome. I would prefer a quick call before they drop down. This is for many reasons. Our availability, if they are elders, then it's a must that both husband and wife are at home. Long journeys undertaken only to find that the home is locked is also disappointing.
Many times we have surprise visitors dropping in, we love it but at the same time embarrassed that there's is very little to offer except coffee/tea and a few snacks. This is even more difficult if it's lunch or dinner time. Being a nuclear family, it's difficult to have something at hand always that we can offer as lunch or dinner for relatives who drop in to give an invitation or see our children or visit us during festivals.
Some relatives from the in-laws side have even taken offense that a decent meal was not offered by the city fellows. If they have to spend the night, its delicate, as some of us have to make arrangements like we shifting to the hall and giving our room or a child's room to the visitors.
Often relatives dropping by from our native place, except to be taken around to see the important city landmark, again we would love to but taking time off work suddenly and arranging transport is difficult, these are minor issues that relatives sometimes take it seriously.
Yes, we would welcome friends and relatives but a call would certainly help us to make their visits and stay more meaningful without us ( working nuclear families) being embarrassed.