By all accounts, Karl-Anthony Towns had a great first year in New York. He was an offensive force, made the All-Star team, and was named to an All-NBA team. That said, he has his flaws, mainly on the defensive end. If the Knicks want to minimize those flaws, starting Mitchell Robinson alongside him may be the best option.
The Knicks ultimately made that lineup change last year in the Eastern Conference Finals, and lineups featuring Towns and Mitchell had a 108 defensive rating, which was better than with either of the Knicks' big men playing alone, or any lineup with neither of them on the floor.
Robinson can mask some of Towns' defensive lapses
One of the most intriguing parts of having Robinson on the floor with Towns is that it allows Towns to guard an opposing wing. In theory, whoever that wing is, will be used less as a screener than the center that Robinson would be guarding.
Last season, according to league tracking data, Towns guarded the screener on 2,761 picks in both the regular season and playoffs, allowing 1.031 points per direct. Meanwhile, Robinson guarded 555 picks, allowing only 0.89 points per direct.
This would give the Knicks a major defensive boost. Robinson is an elite defensive talent who has only gotten more disciplined over the years. He proved he can switch and guard on the perimeter and is an elite rim protector as well. In theory, this should also help to keep Towns out of foul trouble, which he has been known to get into far too easily.
The move will help the rest of the defense as well
Having Robinson alongside him should certainly help Towns. It should also have benefits for the defense as a whole. The Knicks' defense overall was notably better when Robinson was on the floor in the playoffs.
The Knicks have plenty of good to great wing defenders on their roster, in Mikal Bridges and OG Anunoby. Playing with a true rim protector behind them should elevate their defense to new heights. Anunoby, in particular, is asked to do lots of heavy lifting when he is on the floor with Towns as the center.
If Anunoby was playing with Robinson, for one, he wouldn't have to spend any time guarding centers, and even more importantly, could take more calculated risks jumping passing lanes knowing that he has a stronger backline behind him to help out.