@ingalls Years ago, QSLing was much more frequent. If you were active or a contester, doing them every month was a real chore, stacks of mail, significant cost. That's not a complaint but it was serious work that took hours.
I reply to every QSL. I always send QSLs in an envelope because lots of damage occurs in the mail. I only start the process myself if there was something special about the contact. I always include SASE. If it's DX, I look on their QRZ to see what they require for QSLs. Some do cash, some do PayPal. IRCs are not a thing like they were in the old days.
I do LotW and eQSL. I don't respond to email QSLs and that's clearly stated on my QRZ page.
A strange thing I'm running into more and more is people who are on LotW but don't upload contacts unless you email them and request they upload your specific QSO. This seems bizarre. Your logging software will upload everything automatically if you let it.