Example: playing a game. You get a phone call. iOS TERMINATES your game. When call is over, the game starts over and progress lost
To add: Even using built-in apps like camera and get a call... I was videoing an event with my kids and the phone rang. I mistakenly thought it was still recording so I ignored the call until it went to voicemail. Nope, the video stopped recording right when the call began coming through and I lost great footage.