The global objective of the logical and temporal program flow monitoring is defined in IEC 61508, part 7:
To detect a defective program sequence. A defective program sequence exists if the individual elements of a program (for example software modules, subprograms or commands) are processed in the wrong sequence or period of time, or if the clock of the processor is faulty.
We allow monitoring and checking each of the objective (logical sequence and timing) individually. If we want to achieve the highest diagnostic coverage levels, the combination is compelling in detecting potential defective program sequences.