Some people lease subdomains or directories on relatively popular domains because they can get better rankings on these subdomains than with their own domains (for example https://youroffer.populardomain.com) or https://populardomain.com/youroffer).
Google says that this is not a good idea
It seems that this works quite well for some people so Google decided to publish a statement that indicates that this technique might not work anymore in the near future:
We’ve been asked if third-parties can host content in subdomains or subfolders of another’s domain. It’s not against our guidelines. But as the practice has grown, our systems are being improved to better know when such content is independent of the main site & treat accordingly.— Google Webmasters (@googlewmc) August 14, 2019
Overall, we'd recommend against letting others use subdomains or subfolders with content presented as if it is part of the main site, without close supervision or the involvement of the primary site.— Google Webmasters (@googlewmc) August 14, 2019
Our guidance is if you want the best success with Search, provide value-added content from your own efforts that reflect your own brand.— Google Webmasters (@googlewmc) August 14, 2019
It’s not against Google’s guidelines (yet)
This technique is not against Google’s guidelines yet. However, it’s very likely that these subdomains and subdirectories will stop ranking well when Google finds out that they do not belong to the main domain.
If you want to get high rankings on Google, better optimize your own web pages on your own domain. The results will be much more stable then. The SEO tools in SEOprofiler will help you to do that: