Originally Posted by kshastry
2. Say, I buy a return trip from BKK to REP or PNH while in BKK on an LCC, and time it so that the return leg (REP-BKK) coincides with my Indian flight back home. Do I need to pass through Immigration again at new BKK airport to check in for my India flight (on TG) when I arrive from REP?
If by "LCC" you mean AirAsia, note that a) they don't fly REP-BKK, but only PNH-BKK and b) they do not have interline agreements, which means that AFAIK you will have to clear inward immigration, claim your bags and clear customs, and then go check-in again, pay the airport tax, and clear outward immigration to board your onward flight. Of course, if you don't have any checked baggage, then you may be able to get your boarding pass at the airside transit desk, thereby avoiding going through immigration.
Note that the REP-BKK route is served by Bangkok Airways (PG), which is a very fine airline -- though not an LCC -- and which does have interline agreements, an airside transit desk at BKK (well, at Don Muang), and a simple but free-to-all lounge with drinks/snacks and internet access.
I hope this helps,
Michael