Proper usage of log_cron_action()

[Antivirus]

When using function log_cron_action(), the $nextitem parameter... What's it for? Does it tell the php engine to exit the cron script and exec the next cron script in order?

If so, how would you go about logging different cron actions within the same script? Can you exec the function without $nextitem and then on the last call to the function only, include the $nextitem var?

I'm confused, never wrote cron scripts before.
Thanks