Why is just an ID in the URL path a bad idea for SEO?

Question

Why is it a bad idea to have a ID in the URL in terms of SEO? How does this URL http://example.com/user/1234 hurt SEO?

Can someone give me a practical e

Answer 1

See this Do SEO-friendly URLs really affect a page’s ranking? question. Based on the answers, no-one can find any proof that IDs in the URLs has any effect on SEO.