Conifers have one growth spurt per year, which is exactly the light green new growth seen in late Spring.
While the trees can tolerate some loss - think of deer nibbling on them - cutting all new growth is considered harmful as it slows down the growth which puts the trees at a disadvantage. Yes, Christmas trees in the US are often “sheared” in summer and many tips shortened, but the reduced growth rate in this case is desired, leading to a dense tree with the classic cone-shape. In forestry, trees are typically grown for their wood and slowing the growth will diminish the profit. And in the wild, a young tree has to compete with the surrounding vegetation. The rule of thumb when foraging is to pick from reasonably large trees and just one or two tips per branch maximum, the fewer the better. Never pinch the top of the tree.
A few warnings:
- Depending on where you live, picking the tips in the general forest may be forbidden, so check local rules and laws first. In your own property or with permission of the owners is of course ok.
- Make sure you identify the trees. While it may seem obvious, there have been cases of people mistakenly picking and consuming yew instead of the harmless fir or spruce.