Here is the Apple page for messages -Use Messages on your iPhone, iPad, or iPod touch - Apple Support
iMessage and texting using SMS/MMS is the same thing and use the same amount of data. Different text apps have different features but texting is texting no matter what app you use.
.... that doesn’t seem plausible to me. Why would there be that “choice” then? There has to be something more to it. I want to know not just what the difference in data use etc is BUT why would you choose that setting at all?
We can answer technical questions but why someone would use one thing rather than the other is a poll which is not permitted on this forum. To see the usage of data, go to settings>cellular and you can see what uses data and how much.
1. some people do not have unlimited SMS/MMS texting, so may want to stick with internet messaging regardless of cellular data or wifi.
2. many of us DO have wifi at home (and at work, and at all sorts of public places around town) so why bother using cellular data at all when I almost always have access to wifi?
3. some iMessage users do not have an iPhone - they may only have a Mac or an iPad, neither of which are capable fo natively receiving a cellular service SMS/MMS text message. But I can still iMessage them any time over cellular or wifi.
4. iMessage uses strong end-to-end encryption, which SMS/MMS does not. iMessage also inherently allows for very long messages, which SMS natively does not (which can cause problems at times for recipients of very long SMS texts).
5. Future iOS features are likely to include iCloud support for iMessage, so your messages will be archived and retreiveable from your iCloud account (this feature unfortunately did not make it into the public iOS release). SMS/MMS texts are not stored or kept anywhere for you automatically, so unless you are manually archiving them somewhere yourself, when deleted, they are gone.
Regardless of why you may not choose to use it, the whole point is people who wish to can. By your argument why would anybody use Skype, or WhatsApp, or Google Hangouts, or any of the other internet messaging services available and popular?
You can always simply sign out of iMessage and never use it yourself. Unless you sign in with your AppleID and create the iMessage account, you will never receive nor cannot ever send an iMessage, so using it is purely your choice to do so, for whatever reason(s).
Benefits of using iMessage?
