When defending against an attack, do you have to use the same approach that the attacker used? It seems like if the foe is hitting hard Forcefully, you should likewise defend Forcefully. If they are attacking you Quickly, your approach in Defense should be Quick as well to dodge.
Is this philosophy correct?
If not, what's to stop players from spending all day spamming their +3 approaches and nothing else?
In Fate Accelerated, you're free to defend with whichever approach makes the most sense.
So your first instinct is probably to pick the action that gives you the greatest bonus, right? But it doesn't work like that. You have to base your choice of approach on the description of your action, and you can't describe an action that doesn't make any sense. Would you Forcefully creep through a dark room, hiding from the guards? No, that’s being Sneaky. Would you Quickly push that big rock out of the way of the wagon? No, that’s being Forceful. Circumstances constrain what approach you can use, so sometimes you have to go with an approach that might not play directly to your strengths. -- (FAE 18, emph. mine)
Remember that attacks aren't described as just "I attack you," but are made to be something more descriptive. In this sense, you pick the approach which is most appropriate for your character to respond with.
For instance, if you're a professional athlete, and someone slices you Forcefully with a sword, you might defend Quickly, but probably wouldn't defend Flashily. If you're an overweight con-man, and someone punches you Forcefully, you might try to evade Sneakily (if appropriate for your character), but probably wouldn't defend Carefully.
If the attacks are being phrased simply as "[Character] attacks you," then you need to ask your GM to provide more descriptive attacks. You need to know what, specifically, the character is doing before you can respond.
So, what's to stop you from using your +3 for every roll? Well, by the rules as written, nothing. But is it really what your character would do? Does it really make sense for the situation?
If a player tries to execute an action with an approach the character really wouldn't use, it's the GM's job to step in and ask if it's truly appropriate. Remember that you're not playing Fate to be the most powerful character possible, but to create the best story possible - this comes from characters' failures just as much as their successes. If your character succeeds at everything, your character really isn't helping the story.
