I can't even remember how this started (and am too lazy to scroll back).
General Studies was very different 'back in the day' from today's exam. We also had to do a test called 'Test in Written English' (or something like that).
General Studies A level included sections on maths and a foreign language, in addition to science and current affairs.
It was compulsory at my school. We were told that it showed universities and employers that we had a broader range of knowledge and skills than our A level results showed. Whether or not that was true, I don't know. A great deal of curriculum time was devoted to it and we had some very interesting speakers, so I assume the school thought it was worthwhile.
Although it never 'counted' as an A level when offers were made, I expect you remember that most university candidates were interviewed rather than relying on grades. I was very jealous of friends who had offers of two Es, because they had made such an impression at interview. The interview covered topics outside the subject candidates were hoping to study, so general topics were useful. The Oxbridge exams included, as now, assessment of thinking outside the subject area.
General Studies was an attempt to force students to have all-round learning, just as the EBacc does today. As far as I know, no university requires the EBacc, but we are told that the more competitive ones look on it positively.