Is there any reason why daily backups would see a reduction in size?

Hi all,
I just noticed a large reduction in my backup sizes this month with no notable changes on our end (as far as I can think). I’m just wondering if this is to be expected again, or should I be worried about something. @sam, are you aware of any change that would cause this? Here’s a screenshot demonstrating the approx ⅓rd reduction we’re seeing:


Thanks!