Placement

Convenience.

It is like a protocol that happens once u have completed your degree.. It also happens when one university or college is tied up with any associated companies. But there is nothing like companies only recruit candidates through on-campus... So to ans your question it's like an easy way of giving students a chance to enter into the corporate world instead of seeking a job on their own... (A modernised way not like a traditional job hunt) that's all.....