It appears to be a UI thing, but it's an excellent UI thing: it reuses familiar bangs and has an autocomplete/discovery mode for new bang codes.

Marginally quicker to type:

@r vs site:reddit.com

After a few tries, I also find the first more intuitive.

I'm sure it's highly likely google will either heavily deprecate/drop this feature altogether. It's already happened with other query tricks.

Less typing