purpose of PTR record ?

[mark]

forward records, like name A maps to IP address w.x.y.z pretty much
solves the name resolution issue.

what is the extra or special stuff that reverse PTR records are trying
to achieve.

is this true that one of the reasons for this may be:
"for Chat and FTP servers it is useful to restrict access to hosts in
certain zones"
how is this restriction implemented ? (if the above is true)