For a lot of reasons. To stop bad guys mostly.

[ he answers with a shrug and then finally approaches the foam. It definitely made a mess, that was for sure. ]

Not really, it's simple experiment- you mix soap, peroxide and some kinda catalyst like potassium iodide and- [ he mimics a minor explosion with his hands, completely with a little 'pop!' sound for effect. ]

It's really cool when you're expecting it.