Folks,
There is no question that it is preferable to leave the A/P in during turbulence --- and the major reason is physiological, in sever turbulence your eyes are subject to "eyeball bounce", actually the liquid in you eyeballs becoming turbulent and decreasing your visual acuity ---- and moderate turbulence might turn into severe without warning.
But, and it is a big but, if the autopilot can't handle it (admittedly a rare thing with modern autopilots) you better be ready to, and your best has to be good enough.
Old single channel analogue were a horse of a different colour.
Being a devout coward, I put a lot of effort into avoiding severe turbulence over the years, but fly enough hours for enough years --- and you will find bad turbulence --- no matter how hard you try not to..
Worst TS/CB I have come across was one night coming down to Luanda from Isle de Sal, worst non-TS/CB a toss up between down range from the Rockies, and a bad day over the Atlantic, or a bad day on the edge of a jetstream over Japan in winter.
Tootle pip!!
PS: A hint for those still flying B747 Classics --- even in light turbulence, take out the altitude hold and just use the A/P on attitude, if you haven't found this out already, you will be surprised how much of the turbulence was the elevators pumping, chasing altitude.