He's using what to me is the "marching-band" style of left-handed stick-holdin', which I learned at school (ie. as a guy marching with a single snare drum), where the left palm is turned upward. Very few rock drummers seem to use this method -- David Narcizo of Throwing Muses is one I know of -- yet Mr Lovering has always used the Standard Rock Grip (both palms down) as far as I'm aware. (He still does his slow/lazy left-hand thing either way.)
Not that it matters, but it just seemed so weird to me, seeing a 25-plus year drummer 'suddenly' switch like this.
I got into traditional grip over a decade after I started playing...it compliments certain techniques such as ghost notes and double/triple-stroke rolls. Also, some proponents of traditional grip claim it improves fluidity of the motion between hits, which can result in more precise and nuanced playing. Neil Peart started using traditional grip many years after joining Rush to undo some of the rigidity he accumulated from playing along to click tracks in the studio.