There are many battles in the game where defaulting effecting DOES give the player bonus damage. It's just how you think about it mechanically. For many boss fights, knowing when to actually brave and attack is essential. You'll do way more damage if you keep defaulting and healing/buffing, and waiting for an enemy to be at -1 or -2 BP, then chain a bunch of attacks. If the enemy is at -2 BP and you have 3 BP for all your characters, you can basically do 4x attacks + 1x attack before the enemy can do anything again, and still default when the enemy can act again if their attacks hurt. If the boss is getting low on health, you can even do an all out 4x + 4x attack at that stage, and string all the special move buffs along for all the attacks. On the other hand, braving all the way when your BP is 0 and the enemy BP is 0 or higher will probably wipe your party because you'll be taking 4 turns of attacks in a row.