This is a no-brainer for anyone attempting a High Chaos run in Dishonored 2. Going High Chaos means that you’re looking to take down any and all enemies you see in your way, and you’ll definitely need a large health pool for that. Having more health is always useful, as you never know when you might need to flee from battle to take an Elixir. Simply put, more health means you have a higher chance of surviving long encounters.
When you have enough runes, consider getting Greater Vitality as well. This perk will increase your health regen rate, and allow you to regain even more health before you have to drink an Elixir.