Suggestion: When you spare a boss gain like or love

[Elvasat]

There is no benefit for sparring bosses. So it would be nice if we get their liking if we spare them.

[Snortlepig]

I'm not sure how much you've played but there is a boss that will hate you if you spare them. I'm pretty sure a couple of the bosses do change to like when you spare them, but as you never see them again you never really get the chance to upgrade this to the love bonus. Killing people also injects cards into your negotiation deck. Particularly at high prestige this can be fairly damaging when you draw a couple of these cards in one hand.

[Proteus Effect]

If you spare certain bosses in the Story Mode, like Arint or Flekfis, they will hate you. 

If you spare a boss in a brawl, you have a chance of them showing up later and befriending them. You can even hire them for a job if you have enough money.

[Prismaux]

I was so naive thinking that there was a benefit to sparing Rook's bosses. Little did I know that they never show up again and give you their name. And you don't even get their special loot!

[AugustGreen]

Well, actually each boss has Boon/Bane, so there is a chance to get it. For example, in a storyline game as Sal I spared Hanbi (the Assassin) on the day 2 (he will like you for it), and later I met him on timed event (save the friend from death) and earned his Boon. 

[Talyn]

I've seen all of Sal's first bosses [both assassins, both Spark Barons] show up, and I have some of their bane/boons, but... I think you might have a point. I don't think I've ever seen either of Rook's day one bosses pop up again. Admittedly, if you don't kill them, you do order both of them to scram, so that is a thing. Still, it might be amusing if the one you didn't encounter become a road encounter for something beside a boss fight...