My tuppence-worth on this one:
I once flew to the Philippines for vacation (on Etihad), as a non-resident. While in the Philippines, I flew to Hong Kong for a sub-vacation (on Philippine Airlines). When trying to return from Hong Kong to the Philippines, Philippine Airlines insisted on seeing my onward Etihad ticket out of the Philippines, which I had forgotten to take with me to Hong Kong. Philippine Airlines did not allow me to check-in until I had got Etihad to email a copy of my onward ticket to the Philippine Airlines check-in staff in Hong Kong.
I now have (since 3 years) an SRRV visa, and with that you can come and go as you please (no travel restrictions, no need to obtain prior approval for travel, no need to show proof of onward tickets, no requirement to pay the travel tax (you just pay the departure tax)).