Over optimization clearly doesn't stop you from putting h1,h2,h3 tags other onsite SEO optimization factors. Over optimization includes,, keyword stuffing, link cloaking, text hiding.There is a long list of factors. PM me if you want them all. And these techniques are clearly gonna hurt your rankings.

SEO plugins will not harm your site at all.

Sure you can use them still. I personally still use them and have no adverse effect on SEO rankings at all. Even during the new google update.

Yes I agree with seadragon you can still use them, all in one seo is a good plugin, you got to remember seo is still an integral part of ranking in the search engines, and although there is a lot of talk about google changing its algorithms so that over seo sites are getting penalized, to make way for good compelling content to get found, seo will always help to aid people and the search engines to delivering content people want and as long as it is not spammy and you are not taking the piss with stuffing keywords and delivering rubbish spammy content, then you will be fine my friend, hope this helps

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Even if they don't help with SEO, plugins can help you change titles and descriptions way faster.

I ranked(without my intention) a site with all in seo for "greece" in a european language at #4 with 522 million results so for sure it does not affect SEO in a negative way.

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