It's not that we need to wear one all the time. But when operating machinery, sanding, welding, or finishing, it simply is good practice to protect your lungs - for damage is cumulative.
Many do a decent job, but most are uncomfortable to wear because of their weight, make the wearing of eye protection awkward or block your sight lines because the filters hang off the front. But this low profile design and very light weight eliminate all those reasons not to wear one. NIOSH P100 filters are highly resistant to oil and protect against dust, mists, fume, and micro-organisms. Hypoallergenic. Highly recommended.