my thoughts exactly simo
In some cases yes for certain types of dog maybe.
But the point that is being made i think is...keeping the litter tight and straight..no pups throwing too much of bull or collie etc etc..when all he wants is a GSD X Good running dog..not a GSD X Lurcher that could go iether way with what the pups might throw to from the parentage.
If he keeps it simple he know what he,s gonna get more or less...if you complicate the mix with percentages of other dogs etc etc..he might not get what he wants.
Why take any chances ? surely that would be a better outcross for