How does this work? Take the patrol option for example.
If two or three units are spaced apart, the patrol option will have those units retain that spacing from each other, because the patrol command is a back and forth attack move pattern.
Therefore, if this new move command: Reposition, is implemented and it can be hot-keyed as R (if not R then another key if it conflicts with other); then, the units will move to a new point, retaining their spacing. Instead of moving back and forward, they will move to that position, retaining their spacing.
This is subject to formation disruption if you click near the edge of a cliff, because some units would then go high ground, others low ground. Also, if using this near a choke point, then the units would most likely just be running around in similar fashion to ranged units trying to get in range to shoot, if behind an army ball.
Usually, I keep spacing by using the patrol, and before they hit the point, I have to manually hold position or stop.
This way, they do not clump as one ball into a certain location.
Therefore, with this new command, players have the option to gather units together in rally or to block a choke point/opening by using the standard move command; or to retain spacing so as to avoid splash damage, when going into an engagement, by using the reposition command.
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TLDR
Attack move: Moves your army to attack enemies on the way, but arriving to your destination clumped up.
Move Command: Moves your army to the select location, but arriving to your destination clumped up.
Patrol: Back and forth attack move, retaining spacing, does not clump up.
Reposition: Move command with retention of unit spacing, does not clump up.
Benefit
By implementing this new mechanic, all players will have the option to focus more on other things during the match up, instead of time consuming repetition of pre-splitting or spacing. In star craft one, there was little need to split, as spacing was retained.
But now, options to become a ball for massive pushes, or to retain spacing while moving, are available.