Yair just published a long post explaining (a) how he and his colleagues use Mister P and the voter file to get fine-grained geographic and demographic estimates of voter turnout and vote preference, and (b) why this makes a difference.
The relevant research paper is here.
As Yair says in his above-linked post, he and others are now set up to report adjusted pre-election poll data on election night or shortly after, as a replacement for exit polls, which are so flawed.