@fakemoney, the con is a slight increse in foundation costs due to slightly more materials. the sunken lounge is implemented after raising the whole floor around 300 to 450mm from ground level, then sinking the lounge to 0 to 150mm from ground level. another method is to sink the lounge below ground level but this requires basement tanking which if not done well, can result to water seeping up the walls.
As Iron Sharpens Iron, So one Man Sharpens Another.