No professional experience. I'm intrigued by systems of rules with exceptions, and I have pretty good recall for random, mostly useless data. (It's a useful collection in aggregate). Some amount of motive to minimize taxation; the tldr there is if you wanted a super awesome charitable trust, open it in the 80s; and maybe try to figure out how to get startup stock into a Roth account before it's worth much, but this requires prescience to know it's worth the effort. I think there are some brokerages that could offer enough flexibility to do it, but I only looked into it much too late.

I read bogleheads forums and tax questions are usually interesting to me. I don't like filing my tax returns without understanding why everything is where it is.

All that said, discounts aren't income comes up in the context of "why aren't cash back credit cards taxable, but account opening bonuses are" which also touches on 1099 rules because people complain about bank X issuing 1099s for all the bonuses, even when they aren't near the reporting limit. A quick search to verify that gift cards count as income (because they're considered cash equivalent) also reminded me of the name of the W-9 form.