I think technically there's only a certain amount of nights you're `allowed` to spend per term outside of Oxford. (`Oxford` being within 3 miles of carfax tower, iirc.) But in reality, I find it highly unlikley this would be enforced, unless maybe you were failing academically. I mean, generally, how would college/university even know you were gone?
I don't know how much is reasonable or a good idea, but I think it is *feasable* to go home pretty much every week.
I have a fiancé who works full time near Crewe, and lives with her sister. Usually she comes to visit me at the weekend, but for a lot of last year she had medical problems meaning that she was off work and not really up to travelling down on the train all that often. So for atleast one term or so I went to see her almost* every weekend. The train journey usually takes a little 3 hours, with 30+mins either end for getting to/from the station. Id usually go lateish on the Friday/Saturday, stay the night, and come back Saturday/Sunday middayish. I also did a fair bit of music stuff, and in my exams got a strong 1st, coming I think 18/167 in the year. And Im not a late-night worker, im usually in bed by 11. My point being that it IS quite possible to visit home almost* every week without failing academically.
*BUT you need to be flexible. You can't be reliant on that trip hope every week. My personal experience is that Ill only know how much work I have over the weekend on Thursday or Friday. And the amount of work can very drastically from week to week. Some weeks (maybe 2 in 8) I just had too much work to go, and I had to accept that and get on with it. And some weeks I could afford to spend more time than I could other weeks. Its not something you can plan in advance.
It's also going to depend on your timetable. Some people have Saturday tutes. And if you have labs until 5.30pm on a Friday, you might not want to then go on to a 4 hour journey.
Also, obviously, whether this is feasable depends on a lot of things: how far away home is, how quickly you work, how well you're doing academically, whether you can get any useful work done on the train, whether you find travelling tiring, etc.
And also, you have to give up extra-curriculars. If I wasnt spending time with my fiance at weekends, Id be playing in a ton of university bands and stuff. However, if I can't garuntee being always free on Friday nights, Saturdays and Sundays (or whenever rehersals and gigs are), I can't join. Obviously a lot of extracurriculars take place at weekends, and take up a lot of time. Luckily Im part of a more imformal band within college now, so I can just organise rehersals etc around when I know I can try and be free, and when I haven't got much work.
In my experience, other students tend to go home only 1nce or maybe 2ce a term.
Also, I don't think its healthy to be realiant on trips home. Because you don't want it to be upsetting when you have a week with too much work for you to go. When I visit my Fiance, it's kind of for her. If I *needed* to do it for *me* every week, I don't think that would be at all healthy. If youre just visiting parents etc for your own sake, id advise doing it as little as possible. At least at first, until you get used to the fact that its a luxury.
(On the other hand, I know atleast one person who really benefitted from dropping work and going home for a couple of days to recouperate, and to calm down a bit. If you feel you need to go, do. Just don't make a habbit of it.)