Gary Illyes from Google explained two reasons why soft 404 errors are bad. Soft 404s are when a page returns a 200 status okay, but Google thinks that page should return a 404 page not found error. According to Gary, soft 404s are bad because they (1) limit crawl budget and (2) the pages won't likely show up in Google Search....
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Google Explains Why Soft 404s Are Bad
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