On a category you can specify for "No overlap allowed" :
Same category
OR
All categories
And you can set a gap (0-720 minutes).
This gap is used when you have a booking. It could be a sportsclub that have some lanes.
Now you want to book a time-slot for a lane, and you specify that.
But it takes some minutes to prepare the lane after you have used it - or before. This is where you can use the gap. If you set a gap of 10 minutes, then it will not be possible to make an event in the time specified for an event - but it will also not be possible to have a new event that is closer than 10 minutes to the already specified event.