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It is dangerous if you simply move the content to another domain and don't have plans to implement redirects, etc. It isn't "dangerous" if done correctly. A well executed migration may see a drop in traffic for a 2-6 weeks (ballpark) and then things should settle back in to normal levels. It's going to depend on the size of the site and the complexity of the migration (content being eliminated, added, massive URL structure changes, etc). Here are some good migration resources: Domain Migration Checklist Domain Migration Lessons How to Change Domain Names and Keep Rankings