As SMF 2.0 know when to execute the task?
I saw that the function AutoTask is called inside the file Load.php.
It means that every time a user connects to the forum, are controlled tasks to be execute?
SMF doesn't use CRON to perform scheduled tasks.
It basically does use users to perform them when they call a page.
So there is a check to see if there are tasks to run, and obviously checking against the current time for scheduled tasks.
Most of the functions I believe are in
Sources/ScheduledTasks.php
It shouldn't affect the response times too much.
eg when you send a newsletter in 1.x it can send 500 at a time and overload your mail server
While in 2.x it will send 50 at a time and spread out so you don't exceed mail limits.