I am wondering if a disallow directive needs to be issued to robots on pages that will generate:a 403 forbidden error;a blank page, or;a page redirect (to log in page for example).Would not doing so have any impact on SEO of the site?
Would a 403 page, a blank page and a page redirect be indexed by search robots?
seo;redirects;robots.txt;googlebot;403 forbidden
Will they be indexed:403 Error  no, most search engines don't index error pages (assuming they're served with the correct HTTP status code)Blank page  almost certainly not, assuming it is entirely blank (no <title>, nothing).Page redirect  Generally only the destination of the redirect will be indexed (usually this is the intended result), but it depends on the type of redirect. For 301 the redirecting page will be de-indexed in favour of the destination page, however for 302 often both the referring and destination page can continue to be indexed.SEO impactFrom the above, you should be able to see that assuming everything is configured correctly, then in cases (1) and (3) we don't need to do anything else to manage these pages' SEO impact. In the case of (2), we probably don't need to do anything else for a genuinely blank page, though I'd recommend avoiding generating blank pages at all if possible. If not, Disallow is better than nothing, and if you can apply noindex directly to the page either via HTML or HTTP header, better still.