I've always had trouble understanding where Blocks are useful in the Dresden Files RPG (and Fate in general). It seems like a character that can create a Block to save themselves is not going to have any better of a defense than if they use the same skill when rolling to defend. Even worse: if you're going to spend Fate chips or tag aspects to help the Block, you have to spend them before the attacking roll arrives, so spending Fate is a matter of guesswork.
Here's a concrete example, to narrow the scope a bit: I was fighting a magically-amped biker in a museum on fire, and I was up close and personal because I'm more survivable than my fellow party members. My highest skills are Weapon and Athletics, which I was using to good effect in Attack actions and defense rolls. I was spending Fate fairly often (about one per roll?), because the other guy was bigger than me. Given that, is there a case where setting up a Block would help more than Attacking or Maneuvering?