So here's the difference: with a trailing comma, you get a +1 diff to add an item:

```diff
@@ -2,4 +2,5 @@
     huey,
     dewey,
     louie,
+    daisy,
   ]
```

Without a trailing comma, you get a +2/-1 diff for the same:

```diff
@@ -1,5 +1,6 @@
   people = [
     huey,
     dewey,
-    louie
+    louie,
+    daisy
   ]
```