Basically leaving it in my main spending account means there's no dividing line between what I'm saving for that purchase and the rest of my spending money. Moving it into my savings, with the rest of my savings, means there's no dividing line between what I'm saving for this luxury purchase and what I'm saving to, you know, actually save.

In my lizard brain, if I did it that way, from the first $50 I set aside, there would already be enough for the whole purchase in my savings, so there would immediately be the temptation to just dip into my savings and get the item now.

I don't want to start into the practice of dipping into my savings for luxury purchases anyway, so while yes I could do that, it would simultaneously not solve the issue with just leaving it in my main spending account while also opening up the new can of worms of setting me up for buying luxuries with my savings.