LCD is slow compared to micro-controllers. When controllers sends one data/command, LCD needs few micro-seconds to execute that. If controller sends another data/command before LCD has executed earlier one, there will be malfunctioning of the software. To avoid this situation, busy flag has been provided. While executing command or data, LCD sets D7 as high indicating that LCD is busy and can not accept another data/command. Once the execution has been completed, it sets D7 at logic0 and comes in ready state.
So before sending any data/command, we have to check D7 by making RW pin at logic 1. But instead of that we can do one thing. We can provide few micro-second delay required to execute that immediately after sending any data/command. So we can make RW as ground and save microcontroller pin.
I hope this clears the doubt.