Blizzard Entertainment has spent a good deal of time trying to innovate and improve Overwatch at every turn for each platform. For consoles in particular they have plans on adding specific features to help improve the play experience on the Xbox One and the PlayStation 4.
So, in layman terms, what he's saying is that the default setting for the new slider smoother will play no differently than how Overwatch already plays at the moment on Xbox One and PS4. The real change is that the higher you raise the slider for smoothing the lower the analog acceleration and aiming will be. This will mean that you'll have more precise aiming since it will take longer to get to that twitch-like response, but you'll also have to deal with potentially slower times in reaching full accuracy, despite having more precision analog control thanks to the smoothing.
Instant acceleration is essentially the equivalent of raising the DPI on a gaming mouse, so you get instant acceleration. This means that if you're really good at handling analog sticks you should excel with playing Overwatch. Alternatively, if you're using a third-party mouse that emulates analog controls, by turning off smoothing -- or setting the slider to zero -- you'll essentially have near 1:1 mouse equivalent acceleration if you're using a console compatible mouse setup. This could give gamers using third-party mouse peripherals a huge advantage during gameplay.
So in even more layman terms: this update for Overwatch will give console gamers options to play with the kind of precision you would expect from a mouse and keyboard setup on PC, as well as having the option to play more casual with assists in smoothing out the aim.
Either way, console gamers get more options in how they get to play Overwatch. Now, I know some people in the forum thread were asking for aim assists on PC and for these options to be present on PC, but they already are!
If you have a gaming mouse you can usually modify the DPI, thus increasing or decreasing the precision of the pointer. It works the same way as smoothing for the console version. Alternatively, if you run Overwatch on PC with the Steam overlay and you have a Steam Controller you can easily setup the game to work with the Steam Controller (or even an Xbox or PlayStation controller) and you can manually modify the sensitivity, precision, smoothing and aim-type through the overlay menu. So, technically, PC gamers already have this option even if some of the finer details may not be present in the game's options menu.
As for the Xbox One and PS4... the Overwatch update containing the new smoothing and aiming options will be available in the next patch.