Effects of Pre-Election Day Voting on Campaign Strategy (& Spending)

It looks like the percentage of ballots cast before Election Day will markedly increase this year and I’m curious about how this will affect political campaign strategy and spending.

I don’t closely follow the details of the various political campaigns and now that I cast my ballot last weekend (3 weeks+ before Nov 3), I have even less interest in political ads or the candidates, at least until Election Day. I started to consider how campaign strategy and spending will/should be changed as the number of ballots cast grows and the pool of ‘available’ voters shrinks. It seems like the value of campaign spending would diminish as the advertising costs remain the same (or even increases) but the number of still-eligible voters becomes smaller and smaller as the Election Day approaches.

Does anyone have thoughts about this change?