FM is also highly desirable for many Computer Science courses
Pupils who are more interested in logic and the whole language of maths and how it works, are more likely to do well (as opposed to those who are good at doing the calculations)
The top University (Oxford) say it would be helpful. Not essential, not even recommended... Just helpful.
That's often the published position, because they do not want to put off the talented which do not offer FM. In practice, you may well find that nearly everyone the course has it, and it can leave those without it playing catch up in the first term. Always worth seeing if you can find a 'what qualifications joiners really have' for courses DC are interested in