Target Lowest / Highest HP Enemy

Another WTF question...stems from my learning the full-on AA+ game...

Using a full A+ team and an A/AA Hybrid team I was almost always setup on "Target Lowest HP Enemy". It worked well, I could knock out 3 or 4 of the opposing team and win, easy peasy.

Now in the realm of AA+ teams with Health(20) and often 4x combos, take Sin/Undead for example, I'm seeing more "Target Highest HP Enemy". Is this a common tactic? Useful if you have the standard maxed set of skills and more than 3x combo? I've had a fair amount of fights end with leaders still standing and it comes down to who did more damage, so it this method just geared towards those fights?

It is also more effective to use a full attack on a high HP enemy, vs wasting a leader's high attack on a low HP enemy, or worse, on an enemy with only 3k hp left?

Downsides?

Just looking for various bits of info here, I really have no historical data to go on.

I used to have it set to Target Lowest HP, however with quite a few teams using an A+ agi, I have switched to Target Highest Level. Haven't lost to a Mixed rarity Agi+ team yet.

Target highest is usually not good, because if you don't kill a target, it no longer has the highest hp. So your next guy attacks someone else, and so on, and none of your enemies actually get killed.

Target leader can be good in low-bp situations like the battle in the dice event, when lots of people have one strong leader and 4 chaff that just suck up one attack each. Or you can use target skills/highest level in the low-bp case too.