On April 29th, 2005, Apple launched Mac OS X 10.4, aka Tiger. With Tiger came launchd, a new Unix-side job scheduling tool. launchd was intended to replace cron, the long-established (and quite cryptic) tool for such tasks.
And now, a mere nine-plus years later, I decided it was time to give up cron and move to launchd myself. Mr. Bleeding Edge, that's me! (Note: Unless you enjoy the Unix side of OS X and currently use cron to schedule tasks, this article won't be of much interest to you.)
Why now, after so long as a holdout? Primarily because I kept running into issues with cron tasks that needed to do things as "authorized me," such as mounting an encrypted disk image, or even just mounting a network share. Or my Mac would be asleep for a scheduled cron task, and it therefore wouldn't run. (launchd will queue any missed tasks to execute when the Mac reawakens.) Finally, my cron file was getting huge and unwieldy, and making simple changes was fraught with danger of breaking something.
So I dedicated a portion of a recent weekend to figuring out launchd, and migrating my cron tasks to this brave no-longer-at-all-new world. If you're still hanging on to cron, read on to see what I've learned about launchd—maybe it'll inspire you to move, too (or not).