The pros of a sink in the island bench –
You have good space around the sink, stove top opposite, you can stand at the sink and work while looking out onto the dining area and beyond being able to converse with your guests, positioning the sink in the island also means you can have quite a number of people working in the space freely without bumping into each other.
There are some cons –
It is really only for those that can maintain a clean and tidy kitchen, the clutter can build up for all to see and you may have an issue with water on the bench, there is a tradition of positioning the sink at a window with the benefit of looking out which many like.
My feedback from clients is often love or hate, which do you prefer?