Yes it is a good step, it is aimed at making parent company Reliance industries net debt free by March 2021. It is anyday better to sell equity than to be under the burdon of debt and be paying interest and losing a bigger portion of the revenue. With the FDI only the proportional portion of the profit goes to the stake holders without losing additional amount to service the interest of the debt.
Also if the amount raised by RIL is higher than its net debt (including the proceeds from both Jio platforms and stake sale to Aramco in Petrochem along with the amount raised from recent rights issue) it will give them more leverage to be able to pay more earnest money for the upcoming spectrum auction and buy bulk spectrum and invest more on the network infrastructure as well.