These new forward combinations are meant to spread the Leafs' top offensive threats over 3 lines, which could cause fits for the opposition. Scoring was the major problem when the Leafs lost in humiliating fashion to the Montreal Canadiens in last year's playoffs and dividing the top scorers over multiple lines could help to avoid repeating that.
Last season, Matthews and Marner were hard matched against Phillip Danault. Danault and his linemates effectively shut down 2 of the Leafs' most dangerous forwards, leaving Nylander, Kerfoot and the Leafs' bottom 6 to do their best to try to beat Carey Price. Spreading the scoring talent out could be exactly what the Leafs need come playoff time.
If the top forwards are hard matched against a solid defensive line, splitting them could work in 2 ways. First, it lets 2 of them play against weaker defensive lines, and that's good for obvious reasons. Second, it allows the Leafs to send their most annoying forecheckers, Bunting and Kase, to do the dirty work down low, freeing up space for Auston Matthews to do what he does best, which is to put the puck in the net with authority.
This is the perfect time for Keefe to try something like this. The Leafs have been known to slump in January, so a big shakeup will keep things fresh and keep them engaged. The Leafs are currently in a playoff position and in no imminent danger of dropping out. More importantly, they're finally healthy enough to spread their offensive talent out.
It's good to see Keefe try something new. The fanbase's biggest issue with Mike Babcock was that he rarely tried new things. If the Leafs should need to adjust come playoff time, they can at least avoid going into completely uncharted territory with their forward group.