Okay, here we go.
Combat Tactic
This is how your thrall will behave when it becomes engaged in combat.
Hold means that the thrall will maintain it’s position. If it’s following you, it will remain rooted to the spot for combat if you aren’t moving (or, it will move when you move in response to it’s Follow distance). This means that if equipped with a melee weapon - it will only swing once its aggro target is close enough to be swung at. Thrall will not move to pursue - thrall is ordered to Hold. If equipped with a ranged weapon, your thrall will attack its aggro target for as long as that target is within range and within line of sight.
Hold is most useful for guarding archers that are placed upon a perch. If archers on a perch have a Combat Tactic other than Hold - they often will come off of the perch.
Chase means that the thrall will attempt to close the distance to it’s aggro target (on Follow, or on Guard). Simple enough. If your thrall has a melee weapon, it will pursue it’s aggro target so that it can swing the melee weapon. I’ve not really messed with this setting a ton with archers. But I presume the same thing. The archer will come after the target in an effort to fire at it.
For me, Chase is sort of the “default” Combat Tactic. If I want my thrall to do any killing - I really want it to be a go-getter, and get in there to attack. Chase is not recommended for archers on perches (as described above).
Withdraw is odd, and probably the Combat Tactic that I use least. If a thrall is set on Withdraw, it will move away when attacked by an enemy. I believe that all mounts are default set to Withdraw. So you witness the Withdraw behavior when your horse or camel is struck. As mounts don’t fight back, they will move in an attempt to evade an attacker. You will see Withdraw from other enemy archer mobs. When you run up on them to attack, they will take several steps back to get some distance between you and them. Withdraw means exactly that - when your thrall takes damage, they will take the time to take a couple of steps back before attacking again. I believe that most archers will default with this setting when they are first cracked out of the shrink wrap.
Following Behavior
This is how your thrall will behave when actively following you.
Passive means that the thrall will do nothing, even around aggressive targets. Defensive means that the thrall will not initiate violence. But if an aggressive target attacks them, or one of the other thralls or members of your clan, it’s game on. Aggressive means that it’s always game on, no matter what. If an enemy or unclanned player comes into the Attack range parameter that is set, the thrall will begin to attack.
Guarding Behavior
This is how your thrall will behave when set to a specific position to guard (NOT following you). The behaviors are the same as described above for Following Behavior: Passive is nada, Defensive is they won’t draw first blood but they will fight, and Aggressive means it’s kill time.
One thing to note on Passive for both Following and Guarding Behavior - a thrall set to Passive --CAN ATTACK-- if you instruct it to do so (as can a thrall set on Defensive). This can be done by pressing the E key while indicating an opponent or mob in the combat reticle. If your combat reticle aim isn’t great, you can also perform a quick Q lock toggle and then press E to get them going. Otherwise, without any sort of command from you, a thrall set on Passive will keep taking hits until it DBNO’s.
Follow
This is the distance behind you that a following thrall will keep. If you want them right on top of you, set to 5m. If you need a little bit of breathing room, set to 10m. If you want them following you, but waaay behind - set the slider all the way to the right. I find that this is most useful leveraged with your mounts - setting to either 10m or 15m to keep them out of the way of combat.
Attack
This is the distance at which your thrall will consider a target “aggro’d.” This range and the thrall’s other behaviors will determine at what distance to start fighting.
Chase
This is the distance at which your thrall will continue to pursue an aggro target. Set all the way to the left, the thrall will not chase a great distance to attack an aggro target. Set all the way to the right, and they will run the earth after your foe.
Hopefully this detail helps. I actually was looking for this detail too - and had to learn by trial and error.