Is it worth creating a profile with Publons?
This is ultimately a subjective question, but one can ask: what is the value added of publons? Or better, what is unique in publons that is not found elsewhere?

In my understanding, the answer to the latter is none. As a PhD student and early career researcher, you should at some point have your own personal website. Furthermore, you should have an account with Google Scholar. And, something that is quickly emerging and soon to become the standard in academia, you should have an ORCID account. The latter is your unique ID as a researcher, with links to all your research. ORCID is a system developed by a non-profit, academic oriented organisation, and ultimately, it is an open source, community base project. Importantly, they also allow you to add peer reviewing activities, something which was unique to Publons (but not anymore). I can testify that in my academic institution, an ORCID is required, as it is used for departmental evaluation.