IANAL, and pardon me if I am incorrect, but I think what your are talking about is called Retained Earnings.
Depending on the amount of money (i.e. earnings) you wish to retain within the business, amongst other things, it can make more sense to go for a full blown C Corp. Also it depends on your location. For example, in the U.S., there are certain limit amounts for what the IRS deems "excess" RE that are kept in businesses.
- The limit and tax rates depend on the type of business. (i.e. LLC vs C Corp)
- LLCs have lower limits for $ that they can keep in the business than C Corps
- C Corps are taxed at lower levels if they remain within their (higher) limit
However, it should also be noted that C Corps' retained earnings can sometimes be subject to double taxation, depending on what accounting methods and equity/payment structures you use. The links provided should help a whole lot more than I personally can.
There is a good article describing LLC Tax Implications, that may help.
There is also a good article describing RE for corporations
Finally, there is a great article describing the difference between the two.