Occasionally the autothrottle is out of service and we fly without it. It happens rarely but we manage just fine. I can remember only a couple of occasions in the last ten years, but it is no big deal. The other times we might switch it off in cruise are if maintenance ask for us to fill out egt, fuel flow etc. So we deselect briefly to note the values. Sometimes the autothrottle on certain aircraft seems to get out of kilter and wont hold selected speed. A brief disconnection usually does the trick, like with other electronic equipment. There is no complicated process to follow for a brief disconnection, although I think it is reasonable airmanship to press the disconnect once so the red blinking light reminds you it is disengaged.