There’s a saying that one shouldn’t put all of their eggs into one basket because of risk. The danger, however, is the other extreme: scattering and spreading oneself too thin.
Of course, there can be a happy balance.
1) Have as many “baskets” as you can manage well.
2) Focus on the baskets that your customers enjoy the most (and bring you the most return).
3) If something one area isn’t producing, solve the problem or focus your efforts on areas that do provide that return on investment instead.
An example of this is social media:
A new business can be intimated by all of the social media sites out there (there are literally thousands). However, rather than trying to open and manage accounts on as many sites as possible (spreading too thin) or risk everything on one site that might bomb (*ahem* Myspace), it is better to focus on the sites where their customers are and that they can manage well. That way, if one site fails, they can redirect efforts into the areas providing the most return.
Just as it is pointless for a business to be all things to all people (they should be focusing on a niche audience instead), no one can possible manage every social media site well without extraordinary resources.