Your event page groups everyone who hasn't answered under Pending, with one button beside it: Nudge. Each person's row has its own Nudge too.
The Nudge sheet shows the message and who it goes to before you send. The message starts as a plain question with the event in it, and you can rewrite it. Each person gets it on their own, by email, with their own link and a Yes and a No.
Two limits, both per person: nobody is nudged twice within 48 hours, and nobody gets more than two nudges from you. People with no email are listed as yours to share; nothing is sent to them, so send their link yourself.
One more goes out on its own: three days after someone was invited, or one day after when the event is less than five days away, to anyone who still hasn't replied at all. It goes between 9 am and 8 pm in the event's time zone, never after the event has started, and the event page names the day.
So someone who never answers hears from us at most three times after the invite: the automatic nudge and your two. If you nudge them before the automatic one is due, yours takes its place.
Someone who answered Not sure yet gets one check-back instead, by email, a few days after they said it. The invite page tells them which day.
Send reminders, under Actions then Options, turns off the automatic nudge, the check-back and the day-of reminder. It also turns off your own nudges for that event, so leave it on if you want to nudge.
Resend, on a pending person's row, sends the original invite again. It isn't a nudge and doesn't count toward either limit.