Using a Grade Scale Instead of a Numeric Value
When you assign a grade to an assignment you can choose instead to assign it a Scale, such as Credit/No Credit or a scale of Competency. Scales are intended to communicate a degree of success to a student rather than a score.
One way to have a scale grade strongly effect your classroom grade is to use it within a weighted Category. A category worth 20% of your grade could still use assignments that were Credit/No Credit for example. However in order to maintain the relative importance of the scale assignments the category would have to use only assignments graded using the same scale.
Note: By the nature of Moodle's gradebook each step in the scale must have a numeric value of some kind, so to have as little effect on the overall grade each step has a value of 1 point. This is not the purpose of the Scale, rather it is only a requirement for the calculations that occur within the gradebook.