Frequency may also be known as PPI or pulses per inch and is a way to control how many times the laser pulses over a given distance during the cutting process.
The higher the frequency the more pulses you have and the more they will overlap resulting in a smoother cut, however the downside to this is that the higher the frequency the more heat it creates while cutting which can cause melting or charring on certain materials.
The lower the frequency the more the pulses will be spaced out from one another and if you lower it far enough you can even achieve a perforated line.
As a rough guide for all acrylic based materials you should use a high-to-max frequency and for all other materials use a setting equal to 30-50% of your max.
It’s worth noting that the frequency setting will not have any impact on the speed of your job.