Why is iMessage causing certain texts not to be delivered to other iOS devices, it's a hit or miss.
I also did a test. I turned iMessage and WiFi off on my iPhone and then sent my wife a text. She got it but when she replied my iPhone didn't get her response but my iPad did? My iPad w/ WiFi has iMessage on. My iPad didn't get all of the texts though and she has been on iMessage the whole time. I believe that she still has iMessage on her 5c but def no WiFi. If she has iMessage on do I have to have it turned on too? And I thought each iOS device has to have WiFi on for that particlaur device to receive and iMessage?
Is there really a point to having this feature on? I just bought these iPhones, this iMessage feature should be working, this is driving me nuts. I'm so confused.
I went into settings and so some feature that said "If iMessage is unable to send it will be sent as a SMS". Should I just select that?
If you have iMessage enabled, it is the default way to send messages. If you do not enable the option to send as SMS, it'll be the only way the message will be sent if iMessage is detected. So yeah, you probably want to enable that. Wifi is meaningless. It will be sent as data either by wifi or by your cellular data plan. Don't worry so much about the wifi.
The situation you described makes perfect sense. Your iPhone and iPad share your Apple ID. When you turned iMessage off on your phone, you didn't disable iMessage, just the phone's ability to receive it. When your wife sent a reply, her phone detected iMessage. It sent the message via iMessage. Your phone wasn't accepting iMessages, but your iPad was. When you sent her the message, you sent it via SMS. Even with iMessage enabled, you can send/receive SMS. That's how you are able to text with non-Apple devices. Your message sent and she received it.
As far as not getting all of the texts, your iPad likely had a short term network issue. It missed the messages during this time.
The feature is designed for three scenarios. In some places, unlimited text is not an option for plans. In those locations, iMessage will decrease the cost of a plan if you're texting other Apple devices. Another is one you've seen. iPads and iPods aren't all data enabled. By including iMessage, Apple has created a way for you to easily text from devices that do not have a cellular connection without the need for additional apps. They extended iMessage to their last couple of OS X releases allowing you to text Apple devices from a Mac. The third relates to poor cell reception. If you're in a building that doesn't get cell reception, but does maintain a wifi router, you can still pass iMessages but not texts.
As far as a "point," that is up to you. If any of these systems works for you, go for it. If you don't see any of them as useful, it's entirely your choice to enable/disable the feature. Generally, I leave iMessage off on everything except my phone and don't run into many issues. The few times iMessage fails, it sends the message as SMS instead.