Hi Vyshnavi
The datasheet of LCDs demand such delay in between switching of its pins or ports, this might be because such LCDs contain a controller within themselves which further interprets the data or command we send using a microcontroller or something similar, and helps to finaly dislpay the result over a liquid crystal screen. Although this delay thing is very small in value but plays a significant role in LCDs functioning.
Hope this clears your doubt 