The better the sale, the more this applies, but in general the thinking goes that you:
1. Might get a very diligent airline representative who
2. Notices that your ticket is priced well below average
3. Asks questions and does some research
4. You get your own ticket cancelled/downgraded/etc. for yourself, but more importantly, everyone else

Some make the distinction between
1. Those that call the airline while the fare is still live to book/ask questions (why would you ever do this)
2. Those that interact with airline staff while flying the fare (check-in, etc.).

I think #1 is universally accepted as bad practice, and there's a little more debate about #2.