Just that really.
For example in Secondary schools, the years 7-9 are the building blocks that prepare students for the GCSE years. Many children have missed a significant part of this. The ablest students will no doubt manage with 8/9 or even 10 GCSE's and do well. Less able students will probably struggle.
GCSE's are really a stepping stone to get you onto the next stage of study. Would it not be better to allow the less able students to study a more concentrated number of GCSE's? Maybe just 5 or 6? Leaving space in the timetable for interventions with core subjects where necessary.