1. Stairs. Roomba's can't vacuum stairs, so you still need to do those yourself.

2. Stairs, Roomba's can't traverse stairs, so you need one for each floor.

3. Doors. If you want the Roomba to vacuum the whole house, you have to have all the doors open for it.

4. Can't have anything on the floor, the Roomba will either get stuck or avoid it. But I shouldn't have to never leave a backpack on my floor if I want it vacuumed.

5. Corners. Roomba's can't vacuum in corners or in tight areas between furniture and walls. or any other weird geometry. ie: I have a wire shelf. Roomba doesn't fit under it but its easy to use a stick vacuum to get between the wires and to the floor.

And this is before we get to the limit on suction and capacity in that form factor.