[Analog]

Well, on earth there isn't much reason to have them. Space is a different matter entirely. I wouldn't be surprised to see mechs used for space combat on the moon, just because it would be easier to build and maintain them in -6X gravity condition and very useful in that sort of terrain. Transformation would be unnecessary (probably), but land walkers with the ability for short trips into space and orbit would likely be invaluable to a military force.