Need information on Visit entity

[parimal gain]

Hi All,
There is a field named contactMech in Visit entity. At first look it seems
that this is to store the contact information for a visitor who visited the
site. But in current system this field is not storing any value although
visits information is stored.
So can anybody explain the exact purpose of this field and what will be the
value to be stored with respect to anon and registered user, also is this
is only a dummy field or it is functional in current system.
Thanks in advance!!!!!!!!!!