Trees "calculate" which branches to drop based on data they gather as they grow. A competent and experienced arborist knows how to read the tree and simply safely cut off the branches that the tree was already intending to drop so that it doesn't fall on your house or whatever. Inexperienced arborists often ignore this key dendrology fact and may totally butcher your tree. In the process they can create an even larger risk of a tree falling over onto your house during a storm
Imo the title here buries the lede: we've known that trees form tension wood in response to external stress. This study claims to find that trees will form it in response only to their own curvature, independent of external factors even including gravity. They compare it to proprioception. That's neat!
It's called cladoptosis (basically self-pruning) https://en.wikipedia.org/wiki/Cladoptosis
EDIT: since I'm on the topic of bad tree trimming, NEVER TOP YOUR TREES https://www.arborday.org/tree-resources/dont-top-trees