I consider that reinforcements is useful in critical or emergency situations.
Exept when you facing a huge army comanded by a good general and you no have a good position even for atack or defend.
In case of defend... trust in your spears and pry!!!!
Find and take an advantageous position, near the rally point and resist!!!

But, (always are a but), if you are attacking... its another thing.
I usually put in the reinforcements queue in first place a couple of units of heavy cavalry. Why? because they are nominal powerful in meele and nominal fasts. And bringme a time to rally more useful units, to rebuild the front and retake a agressive actitude... meanwhile the heavy cavalry distracs some units and disrupts from they formation.

The tip is what the attacker must attack and retreat, and drive into a trap the enemy units or army.

At last, i hope what my opinions be of your grace.

MAY THE FORCE BE WITH YOU!!!!