There are many mechanics to track the health and survivability of a player character and the creatures they encounter. For the moment, I’m focusing on the Dungeons & Dragons model as it is a pretty simple system and it is mirrored in many others. Hit points, as defined in the 5E Player’s Handbook (pg. 12), “define how tough your character is in combat and other dangerous systems”. Through the editions, they have been treated as everything from blood spurting out to mental fatigue to a more experienced adventurer can just endure more abuse than a lowly peasant. How PCs determine their Hit Point Maximums shapes their experiences and at my table there have been a few different ways that we have done this.
1) Maximum hit points at every level
Makes for a super durable and Heroic level party that you can feel free to open up some serious damage on. Also easy to figure out the maximum hit points. Most encounters have average hit points, but the Dramatic Encounters feature a creature with 3/4 to Max hit points as the damage output of the party rose significantly between levels 5 and 7 (currently at level 12). Healing potions, spells, and rolling hit dice during a short rest remain random.
2) Average hit points at every level
Makes it easy to calculate max hit points at a level. Helps out those bad rollers. Makes for a lot of sameness across the PCs for hit points of similar classes.
3) Option to reroll all hit dice when levelling.
If that total exceeds the current total, you get to keep it. If you choose not to, roll a single die and add it as per normal. Helps even out a few bad hit dice rolls, and those PCs with great maximum hit points usually don’t choose to reroll.
4) DM and player roll a hit die. PC gets the better of the two rolls.
So, advantage and it tends to average higher. As the DM is usually asked to witness hit point rolls, doesn’t seem to slow things down much. There’s a popular podcast, The Glass Cannon – Giantslayer that did this with an added rule of ‘reroll if both rolls are the same’.
5) Player gets to roll, get to take the ‘average’ if they roll less than it.
Slightly beefier PCs, and those players who roll statistically horrible have a safety net.
Conclusion – A Few Words about Recovery
So it’s pretty much a dial of how random or hardy you want your PCs to be. The more epic you want your players to feel about their PCs, err towards higher averages or even max it out. If you want more fragile PCs, keep it random and tinker with the recovery rules, such as recovering hit points only from rolling hit dice (even after a long rest) and adjust how many hit dice are recovered per long rest (full, half, or even a quarter).
The original version of D&D kept it simple with only 1 hit point per day of total rest (though most of us house ruled for 1 hit point per day while exploring, 2 hit points plus constitution bonus per day of full rest). Pathfinder / 3.5 adjusted this slightly by recovering 1 hit point per level per long rest / day. I admit, I like this last one as it levels with the characters and hit points represent more than just physical wounds. A slowed recovery rate adds weight to the magical forms of healing out there and even reducing how many healing potions are found can affect the pace of your game.
Between these two dials of hit points / hit dice and recovery, you can set the feel and pace of the game at your table. What sort of healing and health styles fit your table best? And do you vary it according to the campaign that you might be running?