I assume he meant the spindly branches. I read a lot that one should cut the trunk just higher than the desired base for main branches (Scaffolding) and dormant buds below there will quickly make up for the small branches that were removed. I've done it many ways, but if you start with high branches you can never bring them back down without ruining the tree.

" The guy at the nursery said I should cut off all the "feathers", that the buds at the base would grow out and make better limbs"

For me, it depends on where the feathers are and if there are live buds left after removing the feathers.

If the feathers are where I want the scaffolds, there's no reason to prune them off. Generally they're not though.

If I have a choice, I prefer smaller weaker feathers to larger stronger feathers. The larger feathers grow into scaffolds which can dominate the trunk.