That's a bad example. Knowing what week 4 is is easy ("End of January"). What's week 27? Or week 43? Without looking at a calendar I can only roughly guestimate.
Week numbers are easily compared to your present time. If you are in week 19, and you know you have to finish something by week 27, you can easily calculate how many weeks you have until that time.
I don’t need to know what exact dates week 27 is when reasoning about it, for most purposes, I can just do simple math to calculate how many weeks it is away.
