Energy Transfer has a lot going for it these days.Units of Energy Transfer (ET 0.21%) have fallen below $17 over the past month. As a result, the master limited partnership (MLP) now yields more than 8%. Here's a look at whether it's time to buy the high-yielding MLP. Why is Energy Transfer down?Units of Energy Transfer are down over 15% year-to-date. That slump has come at a time when the S&P 500 has rallied over 16%. The main factor fueling Energy Transfer's underperformance is its slowing growth rate. Th ...