Deprecated? smtpd_tls_session_cache_database

[MRob]

I thought I had read somewhere that modern versions of Postfix you 
shouldn't set up smtpd_tls_session_cache_database but I can't see 
anything in the docs now.

Reading docs still it seems smtpd_tls_session_cache_database can be 
useful. What is behavior when its empty(default)?