The OP is flying to HKT and thus this is a domestic flight. TG C Domestic allows you acess to the TG Domestic Lounge. I haven't visited the domestic lounge at Suvarnabhumi yet, but the old one at Don Muang was nothing to get too excited about but was preferable to sitting around in the main terminal. Given the state of Suvarnabhumi right now lounge access takes on a whole new level of importance.