Let me get this **** straight 250w bulb in a 400w ballast?

man ive been reading and reading and reading some people say some crazy ass shit that its gonna blow and all this crap but i wanna know for sure wtf makes it so dangerous its just using less power to power the bulb which relieves stress on the ballast as well here are some of the topics i found info in and to be honest i think its possible without any significant damage. in the first topic mygirls demonstrates it and has been doing it for years and all of a sudden all these people pose all these threats???? seriously can i get a straight forward answer ive seen it done in many cases and have proof of it actual videos now there are these fools who say its gonna blow melt last less etc.... where is their proof.........? i respect everyones opinions but i just want a straight answer and cant seem to find it

https://www.rollitup.org/indoor-growing/332038-250w-hps-bulb-400w-hps.html
http://wiki.answers.com/Q/Can_you_use_a_250W_Hps_bulb_in_a_400W_ballast
http://www.uk420.com/boards/index.php?showtopic=138268

bump........