The Brace-Gatarek-Musiela pricing model is also known as the Libor Market Model ("LMM"), which uses market-observable LIBOR forward rates. Because this theoretical pricing model uses what can be directly observed rather than items that more traditionally have been used like the instantaneous short-rate or instantaneous forward rates, and the fact that the model is consistent with the market-standard approach for pricing caps, this model is quite popular with market practioners.