easily readable, writeable, comparable and sortable by software
language independent
can not be confused with other popular date notations
consistency with the common 24h time notation system, where the larger units (hours) are also written in front of the smaller ones (minutes and seconds)
strings containing a date followed by a time are also easily comparable and sortable (e.g. write "1995-02-04 22:45:00")
the notation is short and has constant length, making data entry and table layout easier
date notations with the order "year, month, day" are already used widely throughout Japan, Korea, Sweden, Finland, Denmark
a 4-digit year representation avoids overflow problems after 2099-12-31
Whether you have been working on your family tree for decades or just this week it is important to standardize the date format that you use. I recommend the International Standard (sometimes known as the ISO 8601) method of recording dates for all your documentation.
Taking the time to study the country and era that your ancestor lived in will help you capture important facts and correct dates for each of them. Knowing a little history and being careful to record the facts exactly as you find them will ensure that your family heritage will be accurately preserved for future generations.
Richard Kearns publishes an informative, easy to use website that helps people discover their family heritage and shows them how to document their family tree for future generations. Go to All-About-Family-Trees.com for more information.