I've recently discovered that apparently lots of people are 'reserving' supermarket delivery slots by just putting a bottle or two of booze which they don't really want into their trolley to take it over £40, and leaving it there for weeks! Then when they're ready to order their actual shopping they edit it and take it out.
Thus just strikes me as dishonest and really very selfish when everyone knows that delivery slots are still in very high demand. I tried to book on Saturday and the earliest slot I could get was Monday 27th. Last week there was a two-week wait and I had to order from my second-choice supermarket instead, where the wait was only a week.
I presume people are doing it the minute their order is delivered, to hold their regular spot for next time. Whereas I tend to be more reactive in my shopping habits, besides keeping a rolling list in my notes.
I feel a bit shocked, but at the same time realise that if I (pre-lockdown) would, say, order on a Thursday for delivery on a Sunday, because that happens to be my preferred day, it's effectively the same thing. But there wasn't a shortage of slots then, going to the shops was no big deal, and I was ordering stuff I actually wanted.
YANBU - it's selfish and sneaky and people shouldn't hog slots; in fact the shops should crack down on it by making it so that slots can only be held for up to a week, and/or make the trolley limit a minimum number of items, not a minimum amount of money. (I know some shops did this for a while but not sure if still continuing.)
YABU - it's really no different from ordering your full shop a few days in advance and editing it several times before delivery as you run out of different things.
(As a side question - when these people forget to update their order and 'accidentally' get a delivery of nothing but a £40 bottle of whisky that they don't even like, should I feel a certain amount of schadenfreude, or be even more annoyed by the totally wasted delivery slot? Or a bit of both? 
)