While trailing calendar periods only show returns for points in time, rolling returns present continuous overlapping increments to provide a more robust view of performance over time. (proshares.com)
They present returns for numerous overlapping (rolling) increments, instead of quarterly and annual trailing calendar periods that only let you see points in time. (proshares.com)
For example, if they were commodities then they may well have out performed over the last 10 year calendar period, but may have lagged every year for the 20 + prior. (allfinancialmatters.com)