Besides toxicity and other reasons to collect weld fumes, such as safety regulations, laser welders need a fume free environment so the laser can perform at its optimal level.
If fume builds up near the laser, the particles within the fume can refract the laser beam, making the process both less efficient and less precise.
It is like driving in fog with your lights on. Fog or no fog makes a huge difference in visibility, this is the same for laser welding as we also use light! Without fume (even invisible) the laser light reaches fully the welding parts without diffraction.
You can weld better, faster and with bigger efficiency with direct fume extraction!!