Using Noindex, Nofollow HTML Metatags: How to Tell Google Not to Index a Page in Search
Hubspot
JULY 19, 2016
Because anyone who finds your thank-you page in search can access your lead-generating offers directly -- without having to provide you with their information to pass through your lead-capture form. There’s also an option to prevent your site from being crawled while still enabling Google AdSense ads to work, if you have them.
28 
Let's personalize your content