Whenever you apply for a grant or submit a publication. You can also add it to your website, CV, or any other place you list your research.
What if I leave Purdue?
Your ORCID profile goes with you. It is not tied to a particular institution. We do recommend that you include an alternative email address on your profile so that you retain access if you leave Purdue.
I already have a Scopus Author ID/profile, is that the same thing?
It is not the same thing, however, you can import your Scopus author profile, among others, into your ORCID profile by following the steps found on the Scopus Profile page.