I think many people would have argued beforehand that twitter in particular was overstaffed, and that you could safely cut large portions of their employees without much loss. In properly run companies, employees are already justified in terms of revenue or other value they bring to the company. If you fire them, you know concretely what the company will lose. Twitter was notoriously unprofitable, and the employees were instead justified in terms of the greenfield work they were doing to bring the company into profitability in the future. Except that clearly wasn't happening, and probably would never happen if they continued down the same trajectory. I don't think there are many lessons regarding that that generalize to other companies. We might carve out a category of company called a "post-startup", being a company that has gone through the startup phase of rapid growth in userbase, but that never moved onto the stage of "established company", owing to a difficulty finding their proper business model. Such a company might reasonably benefit from a large staff reduction. For other companies this is less clear.