Moving content (that is already indexed/ranking) from one url to another

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Alan Bleiweiss: In most cases, the answer is "all at once". If there`s fifty other major site changes being done, and if you`re talking about migrating a large scale of URLs to new ones, it can sometimes be best to split the URL work out separately, yet even then, it`s still almost always wise to just rip the bandage off in one shot, if all you`re doing is URL changes.
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  Jim Munro: It`s not the content that is ranking, it is the url combined with the elements associated with it, including the content. Once you redirect a url, it`s gone and you are starting over with the new url.
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  Neil Cheesman: there have been about 40
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  Alan Bleiweiss: But why submit the old one for removal? Why bother?
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  Neil Cheesman: okay - - then what to do with the old content - just delete from website (it is redirected) OR does G manage to crawl urls even if they are 301 if they are left `live`. (not sure that is possible)
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  Michael Stricker: Keeping a tidy roster of URLs is a matter of good housekeeping. I’ll bet your sock drawer is a model of organization! But, encouraging Google to tidy up its Index is a good thing, especially on high-turnover big ECommerce or frequent-publisher news media sites.
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  Richard Hearne: Never submit old URL for removal. Canonicalisation of signals will only remain in place so long as old URL is published and providing those canonical hints. Same applies to the redirect - never submit URLs for removal unless you have a very good reason to do so.