2 things that I probably would have save scummed in my current run if it wasn't for Honour mode:

1) Not due to a bad roll, but due to missing a dialogue option in a Shadowheart romance.
Asked Shadowheart to tell about herself, but didn't pick an option about "something besides Shar and tadpoles". I thought I'll be able to return to this conversation later, but the line to ask her about herself was gone from that point on and I didn't want to restart a run because of this. Now I can't gift her night orchids and her Act 3 romance scene won't trigger, because it is tied to this one conversation way back in Act 1. RIP sand castles.

2) Failed to convince Astarion not to ascend and refused to help him, which made him mad at me and he left the party.
Playing low Cha fighter, but with Persuasion proficiency, had guidance from Shadowheart and advantage from Lucky feat. DC is 18, total bonus to a roll is 4-7. Used 4 inspiration points. Didn't manage to roll above 16 total even once.