Assuming that everyone always performs a revocation check, do we still need expiration time in each certificate?

I understand that each public key certificate includes an expiration time, and a CRL is issued periodically, listing all currently revoked certificates. However, in class we were told to think about whether or not we still needed expiration time in each certificate assuming a revocation check is always performed. I feel like we would still need an expiration time in each certificate because then, how would we know when a certificate is revoked?

If anyone could help broaden my mindset, it would be much appreciated