What if we use Remove URL from Google Webmaster to remove those indexed old URLs?

JOHN MEULLER (Webmaster Analyst from Google):

That’s something I would only do in situations where the content really needs to urgently be removed. I would not do that for normal site migrations. I wouldn’t do that for normal changes of content within a website. If you’re maintaining it, you’re adding and removing content, that’s not what I would use that tool for. I’d really only use that for situations where you urgently need to remove the actual content from search. Maybe you published some private information accidentally, maybe you– I don’t know– allowed your development server to be recalled or something like that. But I wouldn’t use it for normal site migrations.