For hand sanding,a good dust filter will be fine.If the material is heated up in power sanding/grinding the fumes can make your eyes water,and probably will start embalming your lungs.For those situations a vapor rated filter is a good idea.All this is for safety purposes.Sometimes I laugh at the warnings on things ie.- "Caution ,contents under pressure,open while pointing away from self and others,severe injury or blindness may occur if not opened carefully."That is off of a plastic soda bottle.However,things you breath can do some nasty things to you.There are a lot of guys who said for years that they never wore a mask,and they never had a problem.Now COPD,emphysema,and lung cancer have come around to bite them in the ass.
A cut is and annoyance,losing a finger or two can be a big annoyance,but losing your ability to breath well - THAT'S A PROBLEM i DON'T WANT TO GAMBLE ON !!!