We will make sure that your personalizations don't get indexed but in a sense, personalization can still have a positive impact on SEO.
In fact, it can improve your SEO.
Personalizations are a great way to create a more personalized experience for your visitors. Customizing your content results in lower bounce rates, higher conversions, more social shares, and a longer time on page. All of these are factors that influence your search rank, so improving them will also positively impact your SERPs ranking.
Personalization is not for bots - it is meant to help individual people with a better user experience. Therefore, we will make sure that your personalizations will NOT be indexed by search engines. To prove this, we ran an experiment on several search engines.
Before installing the script, your personalizations are accessible in preview mode. The preview has a canonical tag that points to the original page. Read the official Google documentation for more information on canonical tags.
Bots don't meet "human" targeting conditions. So, instead of displaying your personalizations to them, we sent bots to your original, unpersonalized page.
Like with all other personalization and A/B testing tools, you could abuse Unless to apply black hat tactics such as “cloaking”. Cloaking refers to showing bots and humans drastically different content, just to trick search engines. We strongly discourage you from doing that. Trying to trick search engine bots is never a good idea. As long as your personalizations are on topic with your web page and as long as you are using them to improve site experience, you will be safe.
As mentioned before, Unless makes sure that your personalizations don't get indexed. If you prefer to take matters into your own hands and take control of which pages get crawled, use your webmaster tools (e.g. Google Search Console). Here you can specify which URLs (and URL parameters) bots are allowed to crawl. For reference, here's the official Google article explaining the process.