Pros
AECOM is a large, global company with its hand in a ton of projects. Some of these high profile projects are creating an increase in name recognition. The company is so large that there are a ton of internal resources. This allows for cross-team recommendations and problem solving, rather than having to go outside of the company for that expertise.
Cons
While "right-sizing" your organizations is often prudent, wholesale outsourcing of entire organizations will make for a bad time. AECOM says they are looking forward to the future and are also wanting to integrate more and more technology into their business. They have decided that outsourcing the entire IT department was a great first start. This move will do nothing to help the rest of the business, but will certainly help the bottom line.