In Boyer v. Brown, 2019 ONSC 3011, Ottawa Judge Corthorn explains (at para.16) that it sets the date for calculation of value of net family property and equalization. There could be 5 possible start dates for calculation of valuation. A later start date means higher valuation.
Couples often ‘separate’ but carry on as normal, same house, same Friday night pizza, same vacations etc. Then a few years later, when the fighting starts, one of the parties says, well we weren’t really separated until much later.
Brown started sleeping in a separate bedroom in 2008 when Boyer confessed she was cheating. The family (with three children) otherwise continued as normal. Tax returns were jointly filed, financial decisions were made together, vacations were together. So Corthorn J. rejected the sleeping-separate date (2008) and chose the August 31 2011 date that Boyer (wife) emailed Brown with a draft separation agreement.
Many married couples do precisely what Brown and Boyer did. They do not make a sharp break immediately. As such, continued entanglement likely means later separation date.
hint: if you really want that early separation date, send a draft separation agreement on day 1 and insist upon signature right away.