FSUIPC is only a must have in general, as it gives you a lot of benefits in optimizing/controlling your flighsimulator. It is entremly usefull in controlling/using hardware addons. So we do not say "don't use it", but we say it is not needed for the Airbus, as the Airbus perfectly works out of the box.
Honestly speaking I am confused on your statement above concerning FSUIPC and its usage with Aerosoft's A3... planes. The confusion is because most of the users in the net highly recommending it as a must to have tool. I am flying A320 on FSX:SE most of the time and would highly appreciate some more clarifications on the subject.