exexpat it is definitely the done thing - for better or for worse - for parents to accompany their teenagers, especially on the weekend open days. Sometimes entire families (granny, young siblings), surprisingly frequently both parents, but generally just one. There will be other young people there by themselves, but my daughter found it was hard to actually find anyone else to talk to as so many people had their parents there.
She did two on her own (although dh met her for lunch so she could debrief then), and two with me in the end. She is someone who really likes to talk everything over (and tbh just likes to talk!), so she found it quite difficult not having anyone to chat to all day. I knew lots of parents went these days, but I didn't think it would be quite so bad - she came home from Bristol on a Friday evening and said PLEASE come to Royal Holloway with me tomorrow!
She's perfectly independent with the travelling side of things - she did all her post-offer days by herself and was again surprised how many parents were still there (fewer though). But those days were more focused and she could chat to others more easily, so it was ok.
dd2 is going to Newcastle and Durham with dh (they're then going to watch some bike-racing in Lincoln on the way home, so nice weekend away for them), and she came to Leeds with dd1 and me. For anything else it will depend on where and our availability!
It's a bit of a vicious circle. Beforehand I was quite scathing of so many parents tagging along, but once there are a certain amount, it makes it not so great for the unaccompanied ones. It was quite nice to be able to talk about the universities I saw afterwards with some knowledge, but I'm not sure it made any difference to dd1's perceptions of the places, or to her eventual choices.