A note or contract is an investment with a simple interest calculation and as each payment is paid the amount of interest you are receiving is lower, until at the end of the contract you are left with nothing.
If you have a 20-year note valued at $50,000. You can take that $50,000 now and invest it in the stock market, an average of 12% annual return will increase the investment to over $450,000, after 20 years.
Investing the money in an account that will compound interest can provide less risk and potentially more future earnings on your money than holding a note or contract.