ineth wrote: »
That option doesn't mean that characters get healed when leveling up.
It means that when the game decides how much a character's maximum HP should increase as a result of a level-up, it doesn't "roll the dice" like AD&D specifies, but instead simply assumes the best dice roll.
For example, a Fighter with 18 constitution leveling up from level 1 to level 2, would normally get his max HP increased by 1d10+4. In other words, the number would be randomly chosen between 5 and 14. But if the "max HP on level up" option is turned on, the game would just choose 14.