I haven't done it often, but I've done it. Why not?
Because of where I currently live, I may try rigging something up so that I can tow my road bicycle out to the paved road (about 3 km away) with my mtn bike and a trailer. Then I'd leave the mtn bike and trailer somewhere, ride my road bicycle, and return by way of the mtn bike with trailer. Maybe. I've been thinking about it.
My commutes are often a combination of the two, which is one of the scenarios that a strong steel framed bike like my Surly LHT really shines. It's virtually as fast as a pure road bike, but as capable as a cyclocross bike on the short cut trails I sometimes use.