If your approach is inherently physical, hands separate won't help, because it doesn't help practice "motions," or anything else people who's approach is physical insist have to be practiced constantly.
The purpose for practicing hands separate is not dogmatic; for some pieces the idea "hands separate" doesn't apply, like Bach fugues (the voices are often split between hands). Practicing hands separate isn't an inherently physical practice, it's rather for listening and practicising to shape melodies and passages unto themselves.
It's also to get away from the rote physicalness of practice, and to learn the piece on a different level from the physical. There may be those who will respond, why practice hands separate? You can just play all the parts, and emphasize the one you want to hear. But that just reinforces rote physical practice. It's actually much harder - but better in the long run - to learn parts as if they were separate entities, and not always insist on attaching them to each other physically.
Some music is so simple as to not require this approach (most pieces with Alberti bass), and some is so complicated you have to hear the parts separately to really know it (look at Variation no.11 from the Goldberg Variations).
My overall point relates to the different types of knowledge that go into learning music. The primary source is always aural knowledge, and it should be the one focussed on the most. These days however, the science of playing the piano has overcome the art, and as such, you see most people harping on physical solutions to aural problems.
If you turn in time back to the days of C.P.E. Bach, you will find that the physical plays a minor role in his treatise on the art of keyboard playing. These days, books about playing piano mention the role of creative listening as an afterthought.
Another level of knowledge is the intellectual - you wil hear different names for this, but it means the level where you analyze, conceptualize, identify. This is the kind of the knowledge where if you have a memory slip, you can say, I know in eight bars it modulates to the dominant, and you can improvise your way to the next point. Or this is the knowledge that if your teacher says, "start at the development section," you know and remember where that is.
Yet another is of course the physical, which in my opinion is the most unreliable. The physical level depends on a lot of circumstances being replicable. For those that depend most on the physical, they tend to get tripped up if they have to play in radically different situations: stages with slopes; benches that creak or can't be adjusted; different lighting; even ivory vs. plastic keys. I have seen it all. I don't mean to be overly negative about it, but only to emphasize that if you rely on this and this alone, you are in danger.
Hands separate practices the aural knowledge, or aural memory; and the intellectual. It practices physical on a smaller level, because you aren't practicing the coordination between two hands, but rather the security of one hand alone. But I think the amount it gives to physical knowledge is small enough that it doesn't really count as a method for improving that knowledge.
I hope there is some sense in there!
Walter Ramsey