[SideburnsOfDoom]

I've seen those in restaurant lavatories.

The disadvantage is that when filling a sink e.g. for shaving, the water pools at a line rather than a point. this is obviously not a problem in a restaurant.

See the third illustration "With a flat sink, you need more water to get the same depth" - an angled flat surface would be somewhere between the two in efficiency of water use.

[randallsquared]

I think if I were going to shave this way, I'd use a bowl instead of putting a lot of water into a presumably-not-perfectly-clean sink. You could wash a bowl and put it away after, whereas you'd have to wash the sink immediately before each shave. If the designer of the sink expected using a shaving bowl, the flat bottom would make a lot of sense.

[SideburnsOfDoom]

I've been thinking about why you see these in restaurants, upmarket nightclubs, corporate boardrooms, etc. IMHO it is that:

1) they look impressive

2) They look like you spent money

3) The only task that they're actually used for is washing hands.

This is a different set of purposes from home use. Making your home bathroom look like a nightclub bathroom at the expense of usefulness is a particular kind of folly.

[vacri]

The piping hot water used for shaving is going to kill most wigglies.