Tasks are just triggers of rules. They are also seen as entry points of a macro. But notice that the body of the macro is defined in the actuale rules. A task can be activated by a button in the keypad panel, or just by another rule.
In the second case they are a good alternative to overcome the lack of OR logic in the M1. You can have:
Whenever X and Y and Z, Activate Task_A
Whenever T and U and V, Activate Task_A
Whenever M and N and O, Activate Task_A
Whenever Task_A, Do 1, 2, 3, 4, 5 and 6
This save you a lot of memory and simplifies your programming because you dont have to program events 1, 2, 3, 4, 5 and 6 on the three different conditions.