the advantage is that you have a working internet connection when you land and do not need to go through the hassle of purchasing a real SIM or eSIM in the country.
yes, you are right. I have never encountered it in Thailand even when I did not have a long term visa yet. Thai immigration was only interested in where I was staying. But a few months ago when I checked it for a flight from Frankfurt to Bangkok I mistakenly handed them my passport without the non-O visa (as a dual national I have two) and they immediately asked about the return flight from Thailand.