A number of people have repeatedly stated that smart scope is a visual change that is mechanically the same. This isn’t true in any capacity.
To begin, smart scope improves bullet spread considerably. In previous games, zooming DID in fact decrease spread, but it did so by different means. In previous games, bullets would always land inside your reticule. When zooming, your reticule remained the same size but covered a smaller area due to magnification - this resulted in bullets landing in a smaller area. Halo 5 retains this behavior and couples it with actually shrinking the reticule, which adds a second accuracy bonus.
The glorious return of descope is much less glorious than anyone wanted. If you’re using a “classic” control scheme like Bumper Jumper, you get knocked out of scope as expected. If you are using the default controls (left trigger to zoom), however, you don’t really get punished for getting hit while in scope. Holding down the trigger forces you to immediately rescope, which renders the mechanic a bit useless.
Finally, there’s a huge delay in scoping in and out. This limits the effectiveness of the scope considerably.
A year ago, I recall a topic where someone suggested ADS in Halo. That person was laughed off the forum. Here we are now - ADS is in Halo.