There are other futures markets that are bootstrapped off of the day-ahead market. Weeks/months out are used to schedule maintenance operations. Years out are used to schedule construction/decommissioning.

So if the extended market prices are high enough, then this acts as a signal to add generation and/or distribution capacity. Likewise, if the extended market prices are low enough, this acts as a signal to retire capacity that has a higher operating cost/lower profit margins.