Offset financial years mean your finance people aren’t working furiously between Christmas and New Years getting the EoY stuff done. I feel bad for the ones in my company every year.
Well, 52 weeks is 364 days, and a calendar year is 365.5±0.5 days, so if you are doing “years” by whole numbers of weeks and don't want to get more than a week out of sync with the regular civil calendar, you are going to need a 53 week year every few years, regardless of your start date.