All I'm going to say is this:
1. you aren't supposed to sit like a pudding, but support yourself with your core muscles & if necessary your legs;
2. it is the way the police are taught to ride in the UK & the way I have been shown to ride by police instructors teaching advanced riding;
3. it is a less tiring way to ride and allows quicker reactions for gear changes and use of the rear brake. It also facilitiates better slow speed control;
4. it is not a sports technique (so is not "cool"

), but most commuting & road riding doesn't require sports techniques;
5. there are lots of ways to ride & lots of debates (if you want them) over all sorts of aspects of how to ride. If I have to choose between someone's opinion of "bad" on the internet & a variety of instructors I know who all have admirable ability, then I know what my choice is going to be.