In finance, diversification is a technique that mixes a variety of different investments to manage risk. The basic idea is to balance risky investments against safe and expensive against cheap. In theory, underperformance by some of the assets will be neutralized by over performance from other parts of the portfolio. This method can be applied to football roster construction.
Scanning the Baltimore Ravens roster of players currently under contract or team control, you will notice the offensive two-deep is relatively young at receiver, running back and along the offensive line while the defensive depth chart features aging starting outside linebackers and safeties.