It's an easy way to let the hotel know your expected arrival time. It also lets you know your room type. Recently, the app showed my UGs at the Bangkok CY (larger room, meh), Pattaya FS Resort (garden jr suite), Kuala Lumpur Ren (Lifestyle Jr Suite), Bangkok JW (CL level room) and Bangkok FS (two room suite). Note it will not fully check you into a hotel where you need to show your passport.