For me, it’s value and size.
As a customer, I look at the cost of delivery and have been known (on most occasions) to look elsewhere if I think the delivery is too expensive. If I’m ordering something that’s fairly cheap then no way do I want to be paying for signed for delivery and then waiting in for it.
Our posties never just post them regardless even if they’ll fit through the letter box. they take them back to the depot and it’s a total pain when I can only go and pick it up on a Saturday and it’s super busy because that’s the only time everyone else can go. I’d not bother buying something if I knew that to be the case & i’d look for an alternative. It might seem lazy and daft, but I know I’m not the only one!!
Alternatively- if the item is expensive or I know is too big to fit through the letter box, i’d happily pay more to protect the item (and the seller if something happens to it en-route) and if it wouldn’t fit though the letterbox anyway I’d know i’d have to be in anyway.
My pet hate though is sellers (generally on ebay) who charge WAY too much for postage so they can make a profit on that! As an artist who’s often posting things, I’m well aware of the ball park figure to which things would cost to post, & it drives me mad when I know the postage should have only cost say, £3.50 but they want to charge £6 or £7.
Anyway…that’s my 2 penny worth. Haha