Pros
Easy to look good when not a lot of skilled workers are around, and you know more about the job than your boss.
Cons
You won't always get much help. I was asked to build a job that current engineers did not design or understand. Not very organized. I started as a contract worker, was told the contract was 90 days, then after 90 days I was told it was 6 months. After 6 months I was expected to give up 20% of my pay to hire into the company as a full time employee, Didn't stick around to see how much worse it would get, but nobody was very happy with their job in the shop. Re-designed things engineers did wrong, installed correctly, and was not commended or appreciated for being more responsible than the guy making twice as much as me, and doing less.