Drupal has its own cron implementation straight out of the box. The recommended setup is that you use cron on your operating system to periodically invoke the cron script in the Drupal installation, which will take care of invoking any tasks that have been registered as cron tasks with hook_cron() and hook_cron_queue_info().
The weakness in this approach that Ultimate Cron aims to solve concerns having fine grained control of when and how cron tasks are invoked. For instance, you might wish ti de-prioritise some tasks and have them only run once day, perhaps in the middle of the night, while others you might like to execute every single minute of every single day.
This module also offers a user interface through which we are able to manage our cron tasks and view log messages that are written during execution of those tasks.
Ultimate Cron offers a different hook for us to when defining cron tasks: hook_cronapi().
This hooks allows us to define the exact intervals at which a cron task should execute an it gives us control over the method used to launch the cron task, which has benefits in terms of our ability to handle concurrent tasks.