Johnny was accused of playing pocket pool. He would be doing his monologue and some times would have his hands in his pockets. Whether he was doing that or not, I don't know. It was a quirk of his delivery. He'd take a hand out wipe or grab his nose. Talk to Ed MacMahon or turn the other way to Doc Severinson.
Or allow the outer to get dirty more slowly from indirect contact.
Underwear, t-shirt would be changed daily. The shirt might be worn once before being laundered while the pants would be worn multiple times before laundering.
For some the coarseness of outer garments would be lessened by having an undergarment of softer material. Undergarments could wick sweat. Undergarments could come between a clean body and dirty clothes or clean clothes and a dirty body.
Yes, underwear serve those purposes to keep valuable clothing clean, and keep sweat off them. In older times this was more critical because of the cost of regular garments and the inadequacy of cleansing methods. Today, one might be cautious about suits or good clothing, which is why I wear underwear when dressed for work or in better clothing.
On the other hand, now that everyone has laundry facilities which can be used daily, I see no reason to wear underwear under shorts or jeans - I can wash them immediately if I feel the need. I never wear shirts a second time, so they're either laundered by me or a cleanser's.
I hate being confined, so boxers are my choice when I have to wear underwear. The rest of the time it's commando for me!