There are different methods to estimate terminal value in a DCF valuation. You can estimate terminal value in a DCF valuation using any of the common methods: perpetual growth rate, multiples of earnings, cash flows or revenues or less common methods such as orderly liquidation value; or a fire sale value. The method you chose depends on the stage of the company and expected growth drivers as well as the information available.
Each method has its advantages and disadvantages!
The primary drawback of the perpetual growth rate approach to terminal value is that firms cannot grow forever; ie into perpetuity. The growth into perpetuity assumption is impossible even if, one day, the firm will have 100% market share of all the products in the world!
Another drawback of the terminal growth rate is that the certainty of growth for younger firms is very low! You address this weakness by doing a sensitivity analysis or simulations on the perpetual growth rate.