It matters because it's a little bit of fun. It reminds me of Dada. Not everything has to have a constructive reason for being.

...Boring, Sidney.

And this matters why?

Paris, Rome - probably a strike.

Heat Miser, Good question.

What might be a purpose for a flash mob? Political statement/protest? Take advantage of some sale or other event? Quilting bee?

i think flash mobs would be cool if they actually had a purpose

Flashmobs seem like a very situationst kind of thing - I can see why it might work in France.