Raw macd is measured in price units, so a reading of 3 means something different for a 40 dollar stock than for a 4000 point index. PPO divides by the slow average and multiplies by 100, producing a scale-free number.
That makes it the right choice for comparing momentum across a watchlist, for ranking instruments, or for any rule with a fixed numeric threshold applied to many symbols.
Interpretation is otherwise identical to MACD, including the same indicator-lag and the same tendency to produce crossover signals late in moves. Normalising the scale fixes comparability, not the underlying timing problem.
Related: macd, macd-histogram, rate-of-change, momentum-indicator, indicator-lag