The suggestion in the article might be slightly tongue in cheek, but there is a takeaway point, especially in connection with Inheritance Tax (IHT).
Where a couple are either married or in a registered civil partnership, on their death the value of the estate which passes to their spouse or partner is exempt from IHT.
If the couple is not married or in a registered civil partnership, then irrespective of how long they have cohabited as a couple, assets which pass to their partner on death will be subject to IHT - payable at the rate of 40%, if the value of the estate exceeds the nil rate band allowance of £325,000.
Whilst I would not suggest that you offer this as a reason for wanting to commit to the special person in your life, it is clear that those in marriages or civil partnerships do benefit from tax advantages and entitlements.
Finally, for those who might consider that marriage is not the route for them, it is also worth remembering that since December 2019 a change to the law means that now both same sex and mixed sex couples can form a Civil Partnership.