Once he receives 500 armor scraps, he will upgrade your units:

Seasoned Units (500 armor scraps):
- Increases certain NPC efficiency (graveyard guards, mine guards and patrolling guards)
- Gives players a 10% damage and size increase buff periodically for 2 minutes (Vanndar Stormpike will yell when it is given) https://vanillawowdb.com/?spell=28418 General's Warcry

Veteran Units (1000 armor scraps):
- Increases certain NPC efficiency further
- Gives players a 20% damage and size increase buff periodically for 2 minutes https://vanillawowdb.com/?spell=28419 General's Warcry

Champion Units (1500 armor scraps):
- Increases NPC efficiency by the most it can be increased
- Gives players a 30% damage and size increase buff periodically for 2 minutes https://vanillawowdb.com/?spell=28420 General's Warcry

These are rarely utilised these days but they are very powerful: reaching champion can turn the tide of battle due to the 30% damage buff. In Cataclysm, it appears that upgrading units will provide around a 100% increase in efficiency. For example, a caster mine guardian has 10,000 hitpoints and Fireball's for 5k. When upgraded, the caster mine guardian will have 22,000 hitpoints and Fireball for an average of 13,000.