I would see a specialist if i had a very specific problem. for example, if my lungs are hurting and i’m coughing a lot, my PCP might not know exactly what is wrong. so, i would see a pulmonologist instead.
on the flip side, i would see my PCP if i have a very common sickness, like the flu. if i have a fever and a small cough, it’s probably just the flu. so, it would make more sense to see my PCP first.