One: their outsize effect on innocent ordinary traffic. SF Pride, which is not until Sunday, prevented me from getting to a Symphony concert Friday night. I was running too late for public transit, and I'd forgotten about Pride since I wasn't planning to come up during the weekend, and it wasn't until I was already irrevocably committed to going through the Civic Center area (which was my destination in any case) that there were signs warning of street closures, which weren't taking effect yet anyway.
But they did. I spent an entire half-hour in completely unmoving traffic only 3 blocks from the symphony hall, and only escaped by popping into the space left open by a car that had darted down a wrong-way alley and then imitating the action of the tiger. The open road was the one leading away, so thence I went.