extract from the Airbus Flight Crew Training manual :
THRUST CONSIDERATIONS
Consider the use of TOGA thrust, keeping in mind the following:
• For a FLEX takeoff, selecting the operating engine to TOGA provides additional performance margin but is not a requirement of the reduced thrust takeoff certification. The application of TOGA will very quickly supply a large thrust increase but this comes with a significant increase in yawing moment and an increased pitch rate. The selection of TOGA restores thrust margins but it may be at the expense of increased workload in aircraft handling.