Game designers are sometimes tempted to offer players a way to start over again the game while they maintain their first run. This is a great feature if the game offers multiple choices and big decisions processes. That way the players can explore different facets of the game and keeps enjoying the game over and over again.
Of course, if the second run is too close from the first, it’ll just seem a waste of time. And a faint attempt from the game makers to artificially over-extend the game lifetime at the expense of new features, which is often bad received.
Example : EVE Online‘s alternate characters are a great way to explore the rich skill tree of the game.