I created Umber and Capitar leaders just to let me play against 10+ factions at the same time. I made Capitar leader General and Umber a Bandit Lord, just to diversify my opposition, and they both seem to do pretty well when compared to other factions.

I also made a custom faction from (rebel) wraiths to Kingdom side, with a Noble leader, so now all professions are represented and sides balanced as I play an Empire Beastmaster.    The noble wraith rebels, they usually suck, btw.

It's a blood trait for Mancers.  They have road building and that accuracy bonus.  But the Road building isn't mentioned anywhere, it's super top secret!  Don't tell no one.

Defensively you can get your troops around quicker. Also, being able to lay down the road manually lets you skip some bad spots/routes that the automatic roads use. Like when they go through wildlands or through an AI area when not necessary.