Why Dalga instead of plain cron?
You can have cron emit the cascading event if you want but you often need a system which can "prod" other systems and ask them to do things because of a timing event. In such systems, cron often falls short as the system around it grows.
For local timing of events, cron is a really good tool however, and I wouldn't hesitate about using it there. It is for system-wide events these general job schedulers tend to help.
* Dalga can schedule one-off jobs.
* Dalga has built-in retry mechanism.