Opus 5.5 and Astra are already very good (because of being RL trained at it) most of these. The way I see skills useful are: 1)If they are created to teach how to use a custom and new CLI or MCP 2) They describe gotchas, tips and tricks that are hard to find using simple search or potentially save some tokens for easier to find ones. The OpenAI and Anthropic teams already said to reduce the skills otherwise as they can also waste context space unnecessarily.