I agree with you, but he was using MongoDB and AFAIK, indexing is a must with this kind of db. Actually, I hope that he does not expect a big write load because

I agree with you, but he was using MongoDB and AFAIK, indexing is a must with this kind of db. Actually, I hope that he does not expect a big write load because he seemed to have added the indexes pretty quickly without thinking too much about it... Just to reiterate, with a RDBMS with a decent query planner, indexing early is premature optimisation.