That's a personal decision. See here for information and a link to FAQs.
https://www.irs.gov/identity-theft-fraud-scams/get-an-identity-protection-pin
Previously, you could opt in but not opt out, so it was for life. They have changed it so it is possible to opt out (if you decide it is not for you), as long as you are not a victim of tax fraud. So it is probably a good idea the way things are going.