The Low Voltage Incandescent Lamps "May" run a little better using DC instead of AC (well filtered DC as opposed to AC), but the most apparent reason would be to drive LED type Lamp arrays.
Wish I had a definite answer for you, but not knowing the specifics per installation / usage / equipment types, I can only "Ass-U-Me" these two things!
on the 'Ass-U-Me" word usage!!!
Scott35