In Diablo II you could start a new game while keeping the same character. People did this to repeatedly to go kill some boss monster that could drop good loot, or simply to restart the game at a higher difficulty level after finishing (IIRC in order to play on hardcore, you had to finish the game on normal). If you started having problems in the game you could start a new game, teleport to whatever the latest town that character had access to, and re-do that part of the game to level and possibly find better equipment.
I don't think this is very practical with a real RPG, though. In an action RPG combat and skills are not connected to the story (except maybe superficially, as quest rewards, etc). If your character develops skills or unlocks abilities as an integrated part of the plot, it may or may not make sense to allow those skills earlier. I guess it depends on how Larian designed the skill / level / etc systems, and if they took that possibility into account when designing the game.
