What is buffer size?
Buffer size is the number of samples (which corresponds to the amount of time) it takes for your computer to process any incoming audio signal. A higher buffer size will result in greater latency (delay), and the higher it is set (larger number), the more noticeable it will become. That means that if you set the buffer size lower (a smaller number), then the processing will take less time and the latency (delay that you hear) will be decreased, making it less noticeable.
However, reducing the buffer size will require your computer to use more resources to process the data. So, this is a balancing act: the smallest-number buffer size will be better, but it may tax your computer’s processing power, resulting in errors. If you have a less powerful computer, you’ll likely need to increase your buffer size, both while recording and mixing, to keep from encountering errors. Typically, you’ll want to use the smallest buffer size your computer will tolerate without getting errors.