Well, if Tsar Nicholas II accepts Ito Hirobumi's compromise on partitioning NE Asia (Russia keeps Manchuria, Japan gets Korea), then Japan both doesn't lose a war (since that would avert the Russo-Japanese War) and curbs Japanese militarism (no easy expansion into Manchuria reduces the ease of empire building and doesn't give the military extra prestige, validation, or (over)confidence in Japan's military might).How about averting militarism without having to lose a war?
Plus, it keeps a check on Japanese imperialism into the continent since Russia getting Manchuria and not fighting a pointless war prevents the unrest caused by losing to an 'inferior' nation and the monetary losses associated with the loss in the form of damages and indemnities, which likely butterflies away the Communists (the loss of the Russo-Japanese War made the monarchy even less popular) and might even avert WWI, since Russia ends up in a two front situation with an eastward focus, the way Wilhelm II intended the Russo-Japanese War to go. Russia gets cozier with Germany as a result, or at least doesn't get friendly with the UK, and so WWI as we know it is gone (though a world-scale conflict is getting to be inevitable by 1900).
Japan might still try to interfere in China militarily but, with the above pressure and lack of (over)confidence, they're more likely to be forced down diplomatically or make more compromises instead of having officers independently start wars every few years. They'd be in a better position too, since not having Manchuria means no inevitable battle to the death with China and having an aggressive European on the doorstep given them an easier way to spin the Coprosperity Sphere bit with the other East Asians.