Question

What purposes might there be for implementing an amplifier circuit with a gain near(or reasonably close to) 1 which also doesn’t filter frequencies

Answer 1

It is used to drive low impedance outputs using high impedance inputs.

Let's say if your input is from an digital-to-analog converter that can only source small current(5mA) and you want it to drive a high powered (low impedance) speaker. You'll have to use a unity gain amplifier .

Similarly we will also need a buffer if we need a high impedance source to drive a signal over a long conductor, because high impedance signals are more affected by noise.

And if the amplifier in the next stage requires a good amount of current which the signal source can't supply. If connected through buffer, the buffer can supply the power from its power source.