It can add a common measure
UIUC can read an SAT or ACT beside students from very different high schools. The score may clarify academic preparation when the local transcript is unfamiliar, but its meaning still depends on course access and performance.
It cannot replace curriculum
Major-specific criteria, prerequisite courses and related experiences should drive the score decision more than the campus headline range. Admissions readers can see whether the student pursued the strongest appropriate sequence; a composite does not manufacture missing preparation.
It can reveal a section imbalance
Illinois requests the highest total and subscores but does not create a traditional cross-date superscore in the application field. A section-level plan is therefore more useful than repeatedly chasing a round total without diagnosing the limiting skill.
It cannot predict admission
Campus middle 50% is 1420–1540 SAT and 31–35 ACT, while Grainger reports 1480–1550 and 33–35. The cohort contains admitted students, not a mechanical rule. Students below, inside and above a range can receive different decisions because the application is broader.
It can guide timing
Applicants self-report; official scores are required only after enrollment. The useful final sitting must leave enough time for the route UIUC accepts and for the applicant to confirm that the checklist is complete.
It cannot freeze the policy
For UIUC, current first-year process describes the verified scope. Testing policies, optional sections and reporting instructions can change; the application term must remain attached to every operational decision.