Many financial advisors would suggest investors never place all of their "eggs into a single basket". However, some other (such as Mark Cuban and Warren Buffett) believe diversification can be a burden on the potential of portfolio growth, by placing unnecessary limits on gains:

Where do you stand on this debate?

How might the everyday investor (as compared to the aforementioned billionaires) limit their risk to the potential highs and lows/volatility of the financial markets?

Is portfolio diversification necessary? 

How often should the investor review his or her holdings, and how often should the investor rebalance their holdings?Please share examples in support of your response.