For family snapshots and things of this nature, the rule generally doesn't apply. Those photos are keepers just for the memory of the people involved. You'll be going back to those photos and deleting the poor versions anyhow.
As I've talked about before in the editing process of photos, bad photos are a liability. Even deleting them detracts from the time you could be processing good photos. If you remove the emotional baggage that comes with having the scene fresh in your experience, deleting the photos is just a much quicker decision.
|This street photo sat in my camera for a long time, but jumped out as one of about a hundred on the card that I liked.|
As an amateur, the luxury of taking your time for selecting the best of your photos is benefit. Professionals in many areas of photography are in a push for time and you'll find their opinion of this method to be that it's unacceptable. Professional photographers in artistic fields tend to prefer this method. Even street photographers that minimize all image editing, even cropping, like this method when they have the time for it.
Large capacity memory cards help with letting the photos cook. Today's memory cards are so large that it allows for many shoots on one card. One card can be in the camera while another is in the computer with files awaiting download and editing. It's a simple system.