The benefit is similar to voting in a political election, if one were transparent, and a good deal more fair.

If you are an investor in Steemit, either with your time or your assets, it will be in your best interest to ensure that the best witnesses are "elected". Allowing lazy, or worse, malicious, witnesses to populate the top witness list would be similar to allowing a 51% attack on the Bitcoin block-chain.

In other words, it would be very bad (tm).

Thanks for your question!