Flying clog
In the land of the JAA...
And to answer the question at interview I would suggest the following:
"Both the TODR and the ASDR increase with increasing mass. The MTM at a given runway is obviously achieved by selecting the V1 value so that the TODA and the ASDA are of equal length."
"When both the required distances are of equal length the take off is said to be a balanced field length take-off. The balanced field length take off method is normally used because it gives the highest allowable take-off mass for the available runway."
I am quoting from the BAE notes (thanks to Graham Morris who is in the UAE somewhere I think and flew V bombers)