Under JAR-25 I think there is a requirement to be able to reach max landing weight within a specified time of takeoff, so some aircraft require a dump facility to do this and some don't.
Interestingly, the Challenger series have a fuel dump system for the tail tank which is purely for maintaining the c of g in the event of not being able to transfer it. People have got into trouble using it to try and lighten the aircraft (not very effective - 1250lbs or 3150lbs depending on the model) and getting themselves out of the forward c of g limit with the subsequent landing problems.