In 1.0, the battle log was a far more efficient tool than it is now. The pace of combat was significantly slower, meaning it was far better to keep track of.
However, it could still be a useful tool for healers or even a tank wanting to keep tabs on what effects are on them, their healer, and others.
I have Damage Dealt/Taken by all things disabled, Actions taken and Actions towards on all things, basically anything that doesn't involve Buffs or Debuffs, or anything that might actually be important to be that isn't displayed better by something else, elsewhere on the screen.
However... it could still use some serious improvements. For one, i think that the above should be the DEFAULT setting for it. It's very cumbersome to change all those things, and to experiment with it otherwise is also more time-consuming, and to say the default state is useless is an understatement.
Two; it's still very difficult to read just out of the corner of my eye. Everything important is preceded by flavour text of what happened, and there's no color contrast between what HAPPENED, and the name of the skill or buff or debuff. I can't glance out of the corner of my eye and see what debuff someone lost. Furthermore, the lack of a color difference between GIVING a good buff and LOSING it is annoying. Losing a good buff is not good just because it involves a good buff, so it shouldn't be blue.
My solution; one, you should be able to set different font colors for gaining or losing buffs/debuffs, Casts starting/ending, damage taken by a party member/yourself or by an enemy, basically anything where something's positive/negative status depends on the context of who or what it happens to.
Two- the battle log seriously needs to cut the fat. It needs to act as more of a killfeed, in a way- where it simply shows a name, an icon or small blurb about what happened, and the NAME of the thing that happened. For example:
Gain Buff: Kairi Kokoro ⬈ Regen
Lose Buff: Kairi Kokoro ⬊ Regen
Casting: Kairi Kokoro ↻ Cure II @ Striking Dummy
Casted : Kairi Kokoro ⬈ Cure II @ Striking Dummy
And other such similar examples.