Maths is the basis of all subjects..... you will find EVERY subject you know,, from art to drama to science to languages. Maths has it's inputs.
However the maths subject on it's on is to develop your skills in Mathematics and be used to investigate how something is and how it proves itself than to understand why it is so. e.g. physics theories are produced on the basis of mathematical functions.
So why you feel that you learn and practise the idea?
Because the math you learnt in your pre years in schools was to introduce to you the idea of basic application such as add, sub, divide, multiply. GCSE was to enhance that further and also make your understanding strong from the work you did in your pre years. Now Alevel becomes different..... a lot of people think that it is just learning and practise, even so my chemistry teacher believes that.. BUT it does mean at all that the stuff is useless and has no implication. it feel that way because you have not stuided the subject at a very advance level to undertstand why it is so. If you go on to study it in uni level, then you will realise by the end of your year all the stuff you learnt in alevel.