Bandpass filter BPSK

I have a question concerning BPSK and the bandpass filter that seems to be sometimes placed before the receiver circuit (the receiver is a mixer and lowpass filter).

Basically, from what I've noticed, there is sometimes a bandpass filter before the receiver of BPSK (and other types of receivers too I think). Is the only purpose of this bandpass filter to band limit the signal and basically just improve the carrier to noise ratio? It doesn't actually need to be there does it? It's optional right?

Thanks.