I own umbrellas. Not fond of any of them though. There 4/5ths ridiculous in my experience. They never fully deliver their intended function and always end up smelling like a wet dog by lunch time.
However, if you work in the middle of the Sydney CBD and walk the streets you kind of need one. Not because I care about avoiding the rain (I agree a decent coat will do any day) but rather if youre shuffling down George St for example (a major street in Sydney) on a rainy day - you'll be confronted by a massive, multicoloured, moving tide of angry umbrellas. All travelling at various altitudes and velocities: many completely out control and on the verge of crashing at any moment.
For the unprepared it's a hazardous situation.
So in the absence of owning a broad sword, tasser or mountain lion, one needs to create an exclusion zone around one's self to avoid getting spiked repeatedly. Used in this way the umbrella serves some propose. But again, I'd rather not use one at all. Ban the lot of them all I say and return the streets to hats and trench coats.