postfix postmap, when to use

[dave]

Hello,
    I've got a confusion issue, regarding postfix's postmap and when to use
it. I've read some documentation that suggests you don't need to run it when
making regexp or pcre map types such as in header_checks, yet the
header_checks file supplied with postfix 2.1 suggests to run it. In addition
hash and other types i'm similar confused. Has this changed from 2.0 to 2.1?
Thanks.
Dave.