It means that if you had three trays left in a three by one configuration, you can't remove the middle one, because it would cause the unit to be split into two units.

On 1/16/2017 at 8:53 PM, King Cheesecake said:

Except for the cavalry for some reason. One would think that cavalry would go wide first. :/

I think this will play into thematics. The cavalry can march/charge a long distance with low initiative manoeuvres, the wider a formation is the harder it is to control as it's more likely to be stopped prematurely by a friendly unit or object. Additionally, negating aim for now, it will make it very difficult to kill a mounted hero leading a cavalry unit.