Avantages
The only good reason is job security. They donot throw out people like many other companies. One reason for this is that they have got good clients as of now and the client base is growing. Also as all the clients are international big business organizations which follow well defined procedures in every aspect of business, one gets to learn the process oriented approach early in the career and see its advantages. And salary can be good if you can bargain hard with the HR. Also one can switchover to a different work domain if one shows the required certifications so if you want to move from Windows to say Database, all you got to do is get some certification (by hook or by crook) and then talk with the management.
Inconvénients
The salary is not in comparison to the industry standards. Also there is a very huge disparity in the salaries of same level employees in the company. They dont have any set standard in terms of employee payscale. The salary increments are also linked to the client you are working with rather than your performance. Also knowledge is not much of a benchmark as is the number of certifications during performance appraisals. The initial selection process is also not rigorous with not much stress on the domain knowledge. For freshers or those with very little experience dont expect to be given work according to your interest area or what was promised during the interview. The HR makes a lot of promises that are never kept. Dont in any case go for a verbal promise. Get it in written & signed by Senior Managers. Rest is all luck.