Oliver Ekman Larsson was drafted due to his offensive potential and undeniable puck moving and skating ability, and it's led him to stand amongst the best.
In the last ten years, only a handful of players have produced at a more elite level on the powerplay than OEL; a surefire reason the Leafs signed him this offseason.
As you can see, he's in the upper echelon among names like Brent Burns and 2-time Stanley Cup winner Drew Doughty. While his teams were never in the upper part of the standings save for a couple odd years, Ekman-Larsson never faltered in his ability to make a difference on the powerplay.
If the Leafs want to maximize their new signee, a first line pairing on the powerplay in order to utilize Matthews, Marner, and Nylander could provide a frightening lineup against opposing PK units. He was still able to manage 32 points last year as a member of the Florida Panthers and had a stretch where he averaged nearly 45 points over 6 seasons for a lowly Coyotes team so clearly the talent is still kicking.