[speeder]

You need to avoid drag losses if you are not using air in first place, because then any drag losses is wasted fuel and reaction mass.

But if you are using a air turbine, you can attempt to make it more economical than the losses from drag and extra machinery weight.

This is more for some type of missions though, if you wanted to make a rocket to pluto, then probably the extra weight is bad, but for a orbital space shuttle this is awesome.

I see the optimal path for long term exploration is use such turbine/rocket hybrids to build orbital shipyards, and then use those shipyards already in the orbit to build pure-rocket ships for missions that don't need to start on the planet (like a voyager-like exploration mission, or launching a hovercraft scout to gas giants...)