Is this correct , if no please let me know why ?
The whole purpose of chip select/slave select pin is to have 1 slave device talking at a time, so that all others ignore the data and only the selected chip will receive/process/respond to it. In I2C, for example, you have an address system, where everyone is connected to the same buses and just waiting for master to call slave's ID, slaves ignore the communication with other slaves. In SPI you pull slave's pin down, the slave knows you're talking to it. Everyone else sitting on the same datalines just ignores this communication, their CS is not pulled low, they're not told to listen. So you need a CS signal for every SPI device, which is the SPI's drawback. But it's faster than I2C, that's the advantage. But yes, be ready to spare for pins for SPI CSs.