What’s a gap night, you ask? (Maria asked :))
It’s simply a period of time between two bookings that’s shorter than your minimum nights stay setting. For example, if you have your minimum nights stay set at 3, but there’s a 2-day gap between bookings, that period cannot be booked.
This is just another method of creating gaps when you feel tired of guests :) I, however, think that's a bit unpredictable method, but also an option, if you just need some gaps, but not sure about exact days. If you need gaps on certain days then nothing is better than setting them manually. It can be done in seconds with Pulse app.