Weight training: one set or three?.

Beyond one set, there appear to be diminishing returns, Hass suggested.
"The general thought now is that many people are overtraining with three
sets," he said. Some research suggests that people who perform multiple
sets may see a small benefit — 2 percent to 5 percent — over single-set
regimens. "But is it worth it? It's up to each individual to decide," he
added.