What are the benefits of iMessage?
- Messages are sync'd between all your (Apple ecosystem) devices
- As you say, you can read/respond on your desktop or a wifi-only iDevice
- Optional read receipts (message is marked Delivered)
- Messages can be sent to email addresses instead of phone numbers, making it immune to phone number changes
- If traveling internationally, you can iMessage over wifi and not worry about international SMS charges
- Unlike Apple Jacks cereal, it does taste like Apple.
And yes, many of these points are just restating of the same thing with slightly different use cases.
You realize that many people use snapchat...a half assed picture messaging app that people just scream into the phone, right?
Other people here have brought up excellent reasons to use iMessage over others, but as far as "trusting" you data, Apple is far more paranoid that I would ever be so if losing data or getting hacked is your concern you need to take a look at how bad the alternatives are.
As brasterc says, I find iMessage to be much faster. Further, there isn't really any guarantee that SMS will get there in a timely fashion or even at all either. Over my lifetime, I've had far more issues with SMS than with iMessage.