When creating a group set, you can let students join a group while setting a rule that forces them to stay within their section. This helps instructors teaching multiple sections of the same course who are looking for efficiency in managing student group work. See screenshot below.
The same option is not available when assigning students randomly. See screenshot below.
When selecting the option to split students in groups, a secondary option should allow you to restrict by section. In cases when students are a part of non-exclusive sections (lecture section and lab sections in the same site, for instance), a popup should appear asking how the random assignment should be done by selecting the sections.