No real difference in nutritional value, it's mostly a matter of size convenience. Let me explain- hatchling BPs' first food is usually a mouse hopper (very young mouse
that's fully furred & eyes open), they're just the right size & active enough to interest a hungry BP. (some are even too active ) But when a BP grows to adult size
they often will only eat one rodent per meal, & an adult mouse is not enough food for an adult BP, so as BPs grow to adult size many keepers get them switched over
to young rats of the appropriate size, so that they can feed their BP just one item per meal & it will be large enough for the snake. See? There's nothing wrong with
feeding mice, and some BPs show a marked preference for their taste, but many adult BPs will not accept more than one item at a time.
Rudeness is the weak man's imitation of strength. Eric Hoffer(1902 - 1983)
Gram per gram it's all the same the difference is when it comes to feeding an adult, you are looking at feeding multiple vs one which obviously means easier and more cost effective (not to mention some BP will not take multiple preys)