File locking

Hi,
        I am wondering when I should use file locking, when should I 
specify the lock file, and what the consequences of using file locking 
when it is not necessary.
        In my current recipes, I file lock (without specifying the lock 
file) when I send a message to a folder, and when I auto-append a name to 
my approved email list.
        I do not use lock files for, assigning a message to a variable 
(used for some auto responses), sending an auto-response, and routing a 
message to dev/null.

--Matthew Saroff