It is generally accepted that we use about 10% of our brain.
Only by people who've heard the same urban legend. It's untrue. Even people who believe that urban legend are still using 100% of their brain 100% of the time. Whether it's helping them is open to question, though. ;-)
As Foolestroupe says, think of the military model. Only 10% of the army might be firing their weapons at any one time, but it doesn't mean the other 90% are doing nothing. In the brain, there are a load of areas, each of which has its own speciality (vision, balance, language, image recognition, personality, etc.) and they all work together to make us do what we do.
As with the military model, if we override orders or reports from one area to another, we're going to get odd results. And as with the military model, if some specialist parts of the brain are disabled (stroke or injury, for example), other parts can often take over, albeit not doing as good a job because they've not had the training.
The simple single postulate of beingness not glued in to the material network of the individual body solves multiple complexities with a single postulate.
Trouble is that it doesn't solve anything. By saying that the "soul" (or "seat of consciousness" or "essence" or whatever) is not physically manifest, it's inherently invisible to any sensor or any experiment. And hence it's not provable or disprovable - it can only be an article of faith. That's where Occam's Razor fails, because an article of faith is simple ("I believe it therefore it is so"), where a physical explanation may be very complex.
For example, think gravity. For years, the prevailing wisdom on the sun and moon was that they were carried by gods. Nice simple explanation, and no-one has to wonder why they stay up there, because gods can do anything they want. Then we got the model of a clockwork universe with the sun, moon and planets mounted on spinning glass balls. Still fairly simple, but more complex than gods. Then came Newton and gravitational attraction, and the complexity went right up. Then we got Einstein, and the complexity went up a whole lot more. And even that isn't explaining everything.
My point is that "forcing" stuff into a biological/mechanical framework *isn't* intellectually lazy. It might not be right, but it sets up further ideas that can be tried to see whether they make a closer fit to what's observed. If you suppose body/spirit duality though, the spirit by definition can *never* be observed. In other words, putting forward body/spirit duality is the *failure* to apply intellect, because it presents an intellectual dead end where the answer is "just because".
To adopt the bath analogy, CFM flow of water down a river and good fluid dynamics models will not tell you how it feels to float down the river in a barrel - but it *will* let someone on the bank describe exactly how the barrel will travel and predict every movement felt by the person in the barrel before it happens. The fact that the person on the bank won't be feeling what the person in the barrel is feeling doesn't make the models wrong.
Meantime the biological/mechanical model has been working onwards. Starting from the belief that the human body is just meat, doctors and surgeons have successfully figured out most of how the body works in terms of blood and muscles and how to fix a lot of what goes wrong and is badly put together, in defiance of earlier beliefs that the body was divinely constructed and that life and death were in the hands of the gods. It's taken about 400 years to get this far.
Once you know how the mechanisms of the body work, nerves and the brain are clearly next on the list. Currently these experiments are often at the stage of metaphorically throwing people down the river in barrels and tracking the barrels to figure out how the river flows, but it's putting up some interesting results already, like this one.