The Trough Value represents the absolute bottom of a drawdown. In the context of stress testing or historical scenario analysis (like the 2008 Financial Crisis), it puts a raw dollar figure on the maximum pain an investor would have felt.
While Max Drawdown expresses loss as a percentage, Trough Value translates that percentage into absolute wealth remaining. Seeing that a $1,000,000 portfolio hits a Trough Value of $450,000 is often a much more powerful emotional and planning metric than a simple '-55%' figure.