I think he meant you should repair every machine you should find, right away. Every time you repair a certain number of machines, Kat's reputation rises, which increases her maximum stat potential.
I think I finished Chapter 6 last night. So far:
Had some fun exploring the lost chunk of city. Talked to a scientist and his wife - I assume finding them is some sort of hidden objective? I hope I didn't miss them in a previous chapter already.
New area opened up, and I decided to literally hop the train - and just rode it to the next area rather than taking the shortcut icon. No load times or anything either - crazy impressive. Also found scientist and his wife again.
One thing I'm really finding interesting - there's a tower in the distance that Rusty simply won't let me get close to - he teleports me away every time I try to get close enough to figure out what it is.
The scientist and his wife expand on the story in the game. You should learn more about that tower from the wife (but you'll find out more about it as you progress). They're in almost every location in the game.