Answer by Santosh Kulkarni:
A Sunk slab can be used in the following locations :
- Bath room/toilet/latrine /wash area floor : The floor trap and the drainage lines can be taken within the sunk portion
- Porch slab : here the beams are inverted so that the beams do not protrude down side and a plain surface is available.
- Mid Landing on a staircase : The end beam is designed as an inverted beam so that there is adequate head room available below the landing.