If you increase flaps for your t/o run then the runway is going to be shorter
More flaps will increase your lift and require less runway.
However, there is always a trade off when not using optimum settings for the weight of the aircraft, pax, fuel etc.
The Boeing 747/400 is equipped with a very good FMC and flight director/auto throttle system which should always be utilised to assist with manual calculations.
There should never be a situation where you are unsure of the optimum flap settings for a t/o run as the increased costs of such an error will be reflected in your wage packet
