I take all big fans off. Top to bottom, provided they corresponding node has some leaf to it. If it's super early in that node's development, the fan will be it's source of supply. But once it has some leaf, I clip.
As far as how often, some people hit em right after stretch like now, and then not again till day 45 or so. Whilst others, myself included, tend to hit them at day 21 like now, and continue as fans grow and get in the way of light. So long as that corresponding node is developed.
Your choice really. But it kinda makes me feel like I'm doing something after day 21 other than just feeding and waiting.