At the start of a course, students won't be very skilled. By the end, they'll be skilled. (We hope!)
One way to design the exercise sequence is to have just a few exercises. The differences in complexity between each one will be relatively large. If students keep up, their skills will change in large steps.
This keeps our grading load down, since we only have a few exercises per student. Nice! However, there are sudden, large increases in cognitive load. Some students will climb each step, but others won't. They won't make it to the skill level we want at the end of the course.
An alternative is to have many exercises per student, with small increases in complexity from one to the next.
The cognitive load in going from one step to another is relatively small. More students will climb each step, and make it to the end of the course.