Roles that survive a wipe rule
Honour Mode keeps a single run. A party plan that assumes a reload after a downed character has nothing to reload. The useful seats are a front line, someone who can heal or throw a potion on the same turn, a character whose main damage comes back on a short rest, and someone who can stop a boss from taking a free swing.
Larian's Honour Mode turns save scumming off. A death screen offers statistics, and continuing disables Honour Mode. The Golden D20 is for a clear run.
Legendary Actions are an Honour Mode resource. The wiki records them as once a round, often when the creature is damaged, and blocked while the creature is fleeing, incapacitated, stunned, unconscious, or restrained.
Haste on Honour Mode
A lot of published parties assume Haste gives a second full attack action. Honour Mode keeps the extra action and takes the extra attacks off it.
Community Update #25 says some powerful unintended exploits are removed on Honour Mode and left in place on the other difficulties.
The Extra Attack page records the in-game result: Hastened and Elixir of Bloodlust grant an extra action that does not trigger Extra Attack on Honour Mode. Action Surge still does. Outside Honour Mode, those extra actions can trigger Extra Attack.
Deepened Pact (Pact of the Blade, warlock level 5) adds an Extra Attack that stacks with a martial Extra Attack on Explorer, Balanced, and Tactician. It does not stack on Honour Mode. Two martial Extra Attacks never stack, on any difficulty. A level 11 fighter's improved Extra Attack is the fighter feature that swings twice more.
Practice the rules without the single save
The official Baldur's Gate 3 account said on 19 Sep 2024 that Patch 7 lets a new Custom Mode game use Honour Mode rules from the Ruleset dropdown, including on Tactician.
Official site: baldursgate3.game.