Why are reactions involving sulfur dioxide, hydrogen sulfide, the halogens and methylene chloride performed in the fume exhaust hood?

Experiments are usually done under the fumehood because the chemical processes will sometimes creates noxious or toxic gases

unknown chemical reaction could potentially create toxic fumes so generally a safety issue

sulfur dioxide will create a rotten egg smell off the top of my head which is used in order to detect gas leaks, wouldnt want to be smelling that, thinking there's a gas leak, evacuating the building, only to realize it was from an experiment or accidental mixture in the waste bin