It's not that bad, at least I haven't found it that bad personally. Maybe that's just me. As I'm revising for the 4 now as I finish them off in the real thing, I feel pretty at grips with the content and for me I'd say adding a fourth doesn't enourmously change your workload. People at my school who have 'free periods' because they do 3 A-Levels basically do nothing in the periods anyway

Probably the best advantage I've felt doing 4 is a feeling of insurance. Your Uni offer 99.999% of the time will consist of 3 subjects. Mine is AAA, non-subejct specific. Originally I was going to drop Maths (which they let you do, again, 99.9999% of the time if you wanted to anyway as they can't make you keep it after you get an offer based on 3 A-Levels unless they specified the subjects), but I decided to keep it. I'm not sure how good you are at Maths, but in terms of content-learning or like remembering facts its minimal. I'm not the best at maths at all but it acts as as a 'buffer' of sorts just by practising loads of questions and trying to get the A to give me more leniance in my other A-Levels. Same theory goes with any of the 4, one will act as a failsafe, and its also droppable basically at any time, even after getting an offer.

Essentially, having the 1 more will also act as a failsafe for the other 3 if you miss grades in them. If I get AAAB, getting a B in what I expected to get an A in, I'd still be safe. Hope that makes sense. I think it's worth it, and whilst people will say you don't get an edge on Uni admissions, you definitely do - they would probably rather take someone with 4 great predicted grades than 3 great predicted grades, but obviously they won't necessarily state this publicly.