The last couple years I've been seeing a lot more teams set up their 1-3-1 power play this way.
For obvious reasons I first noticed it watching the Leafs a couple years ago. They had a period where they let in a bunch of short handed goals. Keefe adjusted by using this setup.
The objective was to cycle the puck down low to set Matthews up for the one timer in the slot.
I figured Marner on the half wall weak side was to help prevent a breakaway on a turnover. The added benefit is that if the puck squirts out that way he has all kinds of space to operate. The defenders have to respect the bumper shot and tend to double team Matthews so can't get pulled out into the open ice where Marner would be parked.
It's a little more conservative while still allowing for all the scoring options a traditional 1-3-1 provides.