Your present self has to coordinate with your past and future selves. You might want to consciously, on-purpose simulate those selves in your mind in order to do this more effectively.
What does this mean? Here's a more concrete example: should you donate money now, or later? There's a complicated argument here about growth rates of whatever-you're-donating-to relative to inflation, but we're going to sail past that completely and assume you would be better off in some objective-ish sense donating later.
The problem then becomes one of trust in your future self: if you spend your whole life being a person who doesn't donate money to charity, how can you guarantee that the person you'll be after 50+ years of non-donation is the sort of person who will actually donate money at the most appropriate time?...