Why having an enclosure is good for preventing the toxic fume from coming out?

filament
abs

#1

Hello, I read that 3D printers with an enclosure is better for health as they prevent the fume from spreading around the room. I cannot understand the validity of this statement because as soon as the user opens the door to take out the printout, the fume comes out from the printer and spread across the room. So, why having an enclosure is better for health?