Hopelessly Lost on Fills

Can anyone please explain what a posted fill is? Why would I want to redo a posted fill when filling a new envelope. I am looking at the the attached screen shot. Why would I select a posted fill when filling a new envelope?

I think the idea here is that you’ve realised you need an envelope now that wasn’t part of your budget at the beginning of the cycle, but you want to capture expenses before the next cycle. You’d edit the posted Fill from the beginning on the month to capture it so you don’t miss anything.
For example, my husband and I decided we wanted a separate envelope for the coffee and meals we purchase at work, vs our regular “Dining Out” budget. I created a new envelope then adjusted this month’s Fill to move some money into it.
You wouldn’t have to do that of course; you could just create a new Fill for that envelope or even transfer some money in from Unallocated, but you have the option to adjust the current spending plan and still keep the total allocated amount the same.
Many people assign all of their money to envelopes, keeping Unallocated at 0, so in that case adjusting a Fill that’s already posted is a good way to balance the month’s total spend.