Contextual Graphs are a context-based formalism used in various real-world applications. They allow a uniform representation of elements of reasoning and of contexts for describing different human tasks such as troubleshooting and interpretation. A contextual graph represents a task realization. Its paths represent the different ways of reaching this realization, each way corresponding to a practice developed by an actor realizing the task. In this paper, we revisit the classical distinction between prescribed and effective tasks, procedures versus practices, logic of functioning versus logic of use, etc. in the light of this formalism. We discuss the position of the practice model with respect to the task model using an example involving troubleshooting a problem with a DVD player and another example involving the collaborative construction of an answer, and place this within the context of some other applications developed in the formalism of Contextual Graphs.