The biggest risk of temporary email is not the first signup. It is account recovery later. If you cannot receive a reset email, you may lose access.
Why recovery matters
Many services use email as the final proof that you own an account. Password resets, suspicious login alerts and billing messages often go to the registered address.
When to update your email
If a temporary signup becomes useful, change the account email to a permanent address while you still have access. Do this before adding payment details or storing important data.
Low-risk versus high-risk accounts
Use temporary email for low-risk trials. Use permanent email for anything you plan to keep, pay for or rely on.