Blocked days are done pre-emptively. Consider: many changes aren't instant. They can take hours to complete. What if things start to happen when you're half way

Blocked days are done pre-emptively. Consider: many changes aren't instant. They can take hours to complete. What if things start to happen when you're half way through? Simpler to just stop making big changes that aren't 100% required to happen just in case. If it can't wait, approvals from someone senior who agrees it can't wait suffices. (Source and bias note: AMZN for 8 years).