Sometimes your material flows and your procedural tasks are one and the same. For example, you can't measure the absorbance of your samples until you've prepared those samples, so your process might look like this:
Different sampling techniques could result in different absorbance measurements, and tasks allow a detailed definition of the required operator workflow to be captured:
Procedure tasks can be re-ordered within the task list displayed for each step.
It is also possible to represent each of these procedural tasks as individual steps, however this would cause an unnecessary increase in steps and design complexity:
There's no correct answer to the question of when to use a task vs a step. The recommendation is to aim to simplify the process; if the process and procedure can be effectively communicated using fewer steps and more tasks, that will typically give both Designers and Operators a better comprehension the work performed.