The first point at which grades become important is the GCSE at 16 - perhaps they might start playing the game at 14/15 when choosing their options, but I don't this being the case all their life.
I have students who are excellent at both Computer Science and Systems & Control, who are not opting for the subjects at GCSE. Many have stated that they have chosen a softer subject to study that will give them some respite from study.
With most students being forced to study 3 Sciences, Maths, English Language, English Literature, a Foreign Language and a Humanities subject, there is little wonder that they want at least one subject, from their optional choices, that they deem easy, if not particularly worth while.
All of which are effectively meaningless for the pupils, only possible consequence might be the set they're given when they first enter secondary school - which should be readjusted very quickly if incorrectly assigned.
With most students being forced to study 3 Sciences, Maths, English Language, English Literature, a Foreign Language and a Humanities subject, there is little wonder that they want at least one subject, from their optional choices, that they deem easy, if not particularly worth while.