Welcome to Android Central! What device do you have?
Do you happen to have any Developer Options turned on? There's an option that kills any process once you leave it, which really shouldn't be used conventionally (and which is why it's a Developer Option). Also, do you have any task killer apps installed? Some of those apps also have settings to force close selected apps. Task killers in general don't help battery life or performance, so as a rule of thumb, you should avoid them.