After reading the other "points of imbalance" thread my opinion is unchanged that it doesn't have much of a role anymore. I'll quote Tagada:
"Few more things to consider: The micro that ML requires is basically going into range of bricks while turning and starting running away at the same time so the bricks can easily disengage and thus buy the defending player a lot of time to make more units, finish his own experimental, make pds air or w/e. So if you want to attack with ML, then ML looses 100% of the time making it an inefficient investment mass for mass."
So, it's possible to make a defensive ML if you need to rush a t4 to counter an incoming enemy t4, but other than that it doesn't seem to have much use. And generally speaking you are better off making other, more mass efficient units to counter the t4, so it it seems to really have only that use, when the lower build time is critical. And it has to be a map/situation where pd won't work because pd have very low build time per dps compared to t3 units. Even cybran t2 pd with an equivalent dps, have very similar build time, mass cost and much lower energy cost, but a far better range than a ML, so you have to need the mobility to defend multiple critical areas.