An AP is more or less essential for IFR.
One can fly by hand in IMC but the pilot workload is much higher, which reduces safety. In nearly all accidents involving loss of situational awareness, the pilot would not have made the mistake if he had more time to think. The airlines realised decades ago that reducing pilot workload is the key to safety but somehow GA likes to live on in its little rut, to prove it can grow hairs on its chest.
IR checkrides are done without the autopilot to push the pilot to the limit of his ability but one would never fly like that by choice.
Real flying from A to B is done on autopilot the whole time. There is ample opportunity to practice one's manual IMC skills by going up and drilling horizontal holes in some cloud in Class G - not in the airways when under radar control and ATC expect you to fly dead accurately.
Re turbulence, it depends on the AP. Some are good, some not so good. In very bad turbulence I prefer to hand fly because the objective is to keep wings level and maintain constant pitch, not maintain altitude. But very little IFR flight is in IMC.