MRP - "Bucket days" (MRP preferences) vs "Days of supply" (Stock item)

According to the help the BUCKET DAYS in the MRP Preferences and the DAYS OF SUPPLY in the stock item are doing exactly the same, even if they have different labels.

If I only use the MRP Preferences (without overriding the days of supply in the item) nothing is consolidated!

Only if I override the “days of supply” on the stock item, the demand of this item will be consolidated.

Is there any purpose behind the “bucket days” in the MRP Preferences?

My assumption was that this is the general set up for all “MRP-Items” & the field on the stock item is for overriding the set up for this specific item.