Some apps utilise this kind of feature to prevent others from viewing a screen with personal data displayed (e.g. a second person looking over the user's shoulder). But it also in this case - I hope - has the added bonus of making sure that an out-of-date BG reading isn't displayed when the App Switcher screen is shown on the device. The aim is to force the user to bring the app front and centre and not to rely on any cached frame grab.
Some apps utilise this kind of feature to prevent others from viewing a screen with personal data displayed (e.g. a second person looking over the user's shoulder). But it also in this case - I hope - has the added bonus of making sure that an out-of-date BG reading isn't displayed when the App Switcher screen is shown on the device. The aim is to force the user to bring the app front and centre and not to rely on any cached frame grab.