Yes, CGPA at SASTRA does matter, especially if you have low CGPA. It will affect your placement and as well as other things. But if you are proficient in programming then you can get into companies like Google without CGPA being a problem. If you have a low GPA, you will miss out on the following things.
Apart from these above reasons, GPA matters for other reasons too. While hiring, companies look at your GPA, not to evaluate how much you know. Rather they want to how responsible and committed you are.