I think a good reason to take four is if you are not sure which you want to do, and then you can drop the least fave by (say) December.
Another good reason is if one is FM which can be a lot, and also maths + FM + CS/Physics is very single-focused. DS2 was going to take three inc FM and I talked him into adding a fourth – that turned out to be his fave and degree choice haha and he ditched FM altogether over the summer. Also I believe a few uns for certain courses (med I think) prefer four if one is FM.
Otherwise there is no benefit in taking four. There is certainly no benefit in taking four to the final line. It won't get you better offers from uni. No uni looks for four A levels. All it does is spread you thin and risk ABBB rather than AAA – AAA will get you better offers.
I do think there are considerable benefits to an EPQ (neither of mine did one) – in terms of research, passion, engagement, something to talk about at uni interviews. Not so much in terms of lowering uni offers tho. And again, if YP are being spread too thin, drop it.
ETA: @Beachforever maths, FM, history/Eng lit and biology would cover that, and not be that wild tbh. Lots of med degrees like an essay subject. If FM was a mare, drop it. If you hated it, you would surely hate a degree that needed it. But a lot of maths-based degrees at higher unis do like FM so if that's a possibility it's worth starting it at least.