ctrl+pick-block will replace tools, which regular pick-block will not. ctrl+pick-block will always place the resulting item in the selected hotbar slot, but regular pick-block will fill up empty hotbar slots first. ctrl+pick-block will always create a new item, but regular pick-block will switch to the item (even if it's in the inventory and not just the hotbar) if an item stack of the resulting item is already in the inventory.