Why is the date of separation so important?

The date of separation (or "the relevant date") is the “line in the sand” that the law draws for determining the value of financial assets and liabilities, so this can be a key factor in whether or not a person will achieve the best settlement they can. There may be a dispute between the parties as to when they actually separated, purely for the tactical reason that the date often affects the financial settlement.

To give an extreme example, if one person purchases a lottery ticket and wins the jackpot the day after the date of separation, then all of the winnings are excluded from their ex-partner's claim. But if their partner can successfully establish that they actually separated after that date, then they could claim a share.