It can tell you where you rate as compared with other investors with similar portfolios. (mrmoneymustache.com)
I have gotten much advice from other investors who have done RE in past but their information is not current with today's market. (biggerpockets.com)
This money that I invest, it never actually ends up in the company but rather in the hands of other investors from whom the shares are bought. (money.stackexchange.com)