They're a good idea for disabled or infirm people. No steps to climb over or up on to get in the shower. Everything can sort of be placed all on one level for easier access all round the room.
Also great not to have to worry about the shower cubicle leaking on to the floor. You can pull a curtain over the shower area to stop water splashing across the basin and loo if you want, but that's not really needed if it's quite a large room.
In today's rat race, it's good to walk in, shower and things, and walk out again.