Large client base. Talented people, have "cracked the code" on offshoring development and support.
Cons
For anyone used to working in US-based firms, the culture and politics will be difficult to understand and navigate. Internal policies and systems focus on the offshore delivery center model. Roles in the US do not fit into that mold, and obtaining approvals for simple expenses can require weeks and insanely high approval chains given the size of TCS. I needed approval from a global division head (a CEO direct-report) just to pay for a short training course. Missions of different departments are not clearly defined, so overlap and conflict are common.