iOS cluster control means running many iPhones from one computer: screens viewed together, tasks dispatched by group, results collected in one place.
This one answers: What Makes iOS Automation Scripts Hard? Coordinates, Waits.
Kai ported a three-year Android script to iPhone and stopped the first afternoon.
Not an error，the half-line “wait until this button appears, then tap.” On iPhone there is no such waiter.
He messaged thinking it was a bad install; the issue was mindset，three years on Android automation, first year on iOS scripts, expecting API parity.
Block 1: The phone does not know what you tapped
Android automation often uses the view tree，“button whose text is Login,” “id xxx.”
iOS here: the console becomes a mouse over the cable and injects down/move/up. The OS sees “someone pressed (300, 400)”：not what widget lives there.
Scripts are coordinate taps，measure from screencast/screenshot after setScreenSize matches real pixels (e.g. 1170×2532).
Forget size setup: no error, “success” every time, taps land beside the target，a rack of phones each missing slightly.
Landscape and new models need remeasure. Measure one phone fully, reuse on same models; mixed iPhone 11 and 12 racks fail，different logical sizes.
Block 2: Waits are only time：you choose how long
No element waits，only sleep. Tuning waits takes more time than writing actions.
Beginners minimize waits because “it passed on my desk.” One fresh phone passes; thirty on a rack include two-year-olds on the end.
Same page, good vs bad signal，load time doubles.
Centralize wait constants，do not scatter magic numbers.
Prefer slightly long waits. Thirty extra seconds nobody notices; one wrong run costs ten minutes to redo.
Block 3: Failures must finish cleanly
HID returns matter: success is null/empty string; failure is a message string.
Many callers ignore return values，the next steps run on a no-op until results look wrong hours later.
Simple retry wrapper: check result, retry once, twice fail → drop that device from the batch and log，do not block the fleet.
Sometimes the session dies，picture still there, taps dead. Reset session beats unplugging thirty cables.
Open session at batch start; close at end.
Chinese vs English input
Unrelated to the three blocks but inevitable.
Chinese: clipboard paste，stable. English: key-by-key or paste for speed.
Paste English with extra spaces? Settings → General → Keyboard：turn off Smart Punctuation.
“Blind” tapping has upsides
No view tree means UI copy changes do not break you if layout stays put，fast-moving apps can be easier.
No proxy IPA，no resign/reinstall cycle when scripts change.
Closing
Android scripts find things; iOS scripts measure positions.
The cruelest difference: nothing says “target missing”，it quietly returns success.
At cluster scale you batch-send，weak single-device debug multiplies by rack count.