I.E. elimination of the difference between Reg. Other than the inability of Irrg to swap dice. The primary reason being to eliminate a number of messy rules in the pip system. Probably the single most difficult and time consuming section of the rules to execute properly are the Spontaneous advance rules. Rarely do I see these properly executed, and in play are the rules most likely to inspire some input from the opposing player during their execution.
Most players tend to take the most logical path toward the enemy rather than that most direct.
These rules in my experience inspire more argument than any others. Fleeing broken commands create similar problems. The rules do model a real aspect of warfare. The greater or lesser ability of certain types of armies to coordinate their movements. However I doubt that the rules as they stand are a particularly good or efficacious model of this problem.