In short, no Belgian Malinois haircuts are required. Even so, some people believe shaving a Belgian Malinois coat shorter will reduce shedding and help keep the dog cool in summer. As professional groomers will tell you, though, both these ideas are myths.
Here's why: on double-coated dogs, the shed hairs come from the undercoat. So unless a dog is shaved bald--which is never a good idea!--the undercoat remains and the dog still sheds. The only difference in shedding for a shaved Belgian Malinois is that the shed hairs would likely be shorter.
Neither will a shaved Belgian Malinois be cooler in warm weather. The dog's double coat acts as a natural climate control system, and serves to regulate its body temperature. On hot days, cool air is trapped between the coat's layers to keep the dog from overheating; the same happens with warm air in cold temps. A shaved double-coated dog is without its natural insulation, and will be more susceptible to sunburn and heatstroke--and the dog will obviously get cold very easily. And when the shaved coat does grow back, it'll be uneven and softer in texture.
The only reason to shave any part of a Belgian Malinois's coat is in preparation for surgery or other medical procedures. Your vet will discuss this with you further.
So to anyone considering shaving their Belgian Malinois coat: put those clippers away!