Whats does Machinery do for me?

Machinery: “enhances repairable rate of fortified units”

For those of you who do not understand this, it is similar to when an NPC regenerates its traps and archer towers. The higher your machinery level, the more fortifications will regenerate after being defeated. This is highly useful when an enemy destroys your defenses and then gets a surprise when 75% of your defenses spring back up!

The above is quoted from

http://hods.com/evony/tag/research/