rich p said:
Why do people put plastic bowls into sinks? It seems superfluous to me.
So you can shove stuff in the bowl to soak while you cook, but still pour cooking water etc down the sink...
The question is more 'why would anyone not have a washing up bowl'
BTW, the washing up bowl was invented by accident. A plastic manufacturer, just after the war, was experimenting making shapes and bowls, and one night the char lady, collecting teacups from desks decided that the plastic bowl sitting on a designer's desk was a better bet than the enamel one she normally used to carry the cups in, because there was less risk of chipping.