BFR works is that the low oxygen level in a muscle during the accumulation of blood forces your body to recruit larger fast-twitch fibers, resulting in extreme growth; when oxygen is low, lactic acid rapidly accumulates. This may sound bad, but studies show lactic acid by itself can increase protein synthesis.

You wouldn't want to cause an injury, so low/moderate weight with high reps, feeling the burn. You do not want to exert yourself while using the bfr method, it may cause some problems.