Nursing to sleep

BabyA
So my husband's doctor told him (as a friendly tip I guess) not to let me nurse our baby and let him fall asleep on the boob because then it will make it that much harder when we get to sleep training. We've put him down a couple times wide awake and he's fallen asleep on his own just by chance, but it did get me thinking. Anyone have thoughts on this? My baby is 3 months old. So we haven't started any sleep training, but I know the time will be here before we know it!