You should use a higher RR for smaller/volatile companies but still should demand a large margin of safety. (20% +)
The bottom line is any valuation tecnique is not perfect. IMO opinion Roger's is one of the best.
The margin of safety serves two purposes.
1) If you miscalculate the intrinsic value you have a margin to make sure you don't overpay.
2) It can supercharge your returns. If you are buying a business that is rising in value at a discount to intrinsic value eventually the share price should rise to the value of the business.