Polls are basically a question of intention. It's so easy to answer a question and say "yeah I'd vote for that guy", no effort, some small time input. Additionally, as we have seen, polls can be manipulated by selectively choosing who is sampled, that's just one way.
Voter registration is something more, particularly new voter registration. It demonstrates more about a pending action than answering a question to a pollster. It's also objective, there's nothing subjective in the figures.
Thus, Voter Registration is a metric that is worthy of attention, I strongly advise anyone who is genuinely interested in predicting an outcome in this election to add this metric to their melting pot of metrics.
