As mentioned above, Additional Mathematics is not compulsory for
polytechnic admission. If you are aiming to enter into engineering
courses, it may be beneficial if you take Amaths.
If you are looking forward to go into other courses like
Business, Design, IT & Social Sciences/ Humanities; Amaths is
not required at all.
But having said all, even if you do not take Amaths, it does not
reduce your chances of getting into an engineering course, nor is
there 'priority'. Basically it just helps you in learning certain
mathematics modules. If you do not take Amaths, polytechnic do
provide bridging programmes for non-amaths engineering
students.
Of course, no matter what you do, just do well in everything
:)