This is a good question. Below is the the explanation of how it is used:
A one-line description used by the device to identify the app for the user.
On Android the titles appear above the task manager’s app snapshots
which are displayed when the user presses the “recent apps” button.
Similarly, on iOS the titles appear in the App Switcher when the user
double presses the home button.
So in short:
On Android: it is used in Recent apps
On iOS: it is used in App switcher
Update 11th Feb, 2020:
The document is updated (I don’t know exactly the updated time)
A one-line description used by the device to identify the app for the
user. On Android the titles appear above the task manager’s app
snapshots which are displayed when the user presses the “recent apps”
button. On iOS this value cannot be used. CFBundleDisplayName from the
app’s Info.plist is referred to instead whenever present, CFBundleName
otherwise. To provide a localized title instead, use
[onGenerateTitle].
So this value has no effect on iOS