Susan Hogarth was just explaining the voting procedure:

Everyone, including delegates AND alternates, gets to vote.
If all the delegates from a state vote, then the alternates’ votes don’t count.
But if not all the delegates from a state vote, then the alternates’ votes count in one of two ways:
1) If the state chose a “ranking” scheme, then the ranking alternates’ votes count (i.e. two delegates don’t vote; the top two ranked alternates’ votes count); OR
2) Random alternates’ votes are selected by the app for missing delegate votes.
As the convention drags on, there will likely be a number of delegates who get tired, or need a break, or whatever, and who miss votes.
So your alternate vote may very well make the difference. And you can do it from your computer/phone at home.

Imported from the original KN@PPSTER