There’s no telling. No rule. No theory. Rule of thumb: does it affect the relationship badly?: considering not doing it. Vice versa: why not.
And so forth. To me, there’s no moral to it.
(Since there’s no real telling due to the multitude of ways for relationships to exist, it probably won’t add too much of interest, but if you asked me, I’d say it may definitely be of healthy value to our relationship, since we’ve lived 24 hours a day only a few meters away from each other, for 9 years now. But that’s me/us. Other people – especially busy bees and intensive career builders may benefit of staying together more during vacations.)