Its very stupid. You can take one day out of your life to visit a place which will be your home and place of study for the next three years (potentially four or five depending) or you can leave it up to chance? When I visited universities, I was looking for a feeling of 'Yeah I can see myself being here' or 'Yes I want to be here!'
I did exactly the same thing last year and applied to universities without visiting them, I was settled on my offer to study History at the University of Bristol, but eventually I did visit the university but only after I'd made my choices. It turned out that it wasn't for me, I got there and felt nothing for it. A year later, on my gap year, I visited three universities to see if they were for me, two of them were, I had a gut instinct and fell in love with them. That's why its so important because your decision on your choice of university shouldn't be based on league tables, "prestige" or being a Russell Group, it should be based on your individual connection to a university that is suitable to you.