Keeping the clutch pedal depressed at stoplights leads to premature wear of the release bearing (also called the throwout beraing). It could also have contributed to your failed master cylinder.
Whenever the pedal is depressed, the master cylinder pushes fluid to the slave cylinder which, under pressure, forces the release bearing against the spring-loaded radial “levers” of the pressure plate assembly, lifting the prssure plate and allowing the clutch plate to no longer be “clamped” to the flywheel. Everything in that system is under load.
In addition, remember that the pressure plate assembly is bolted to the flywheel and continues to spin with the engine. That means that not only is the release bearing under axial load, but its outside race is spinning while its inside race (on the tranny input shaft) is stationary.
In short, when you hold the pedal in you keep the reelease bearing in its loaded state and the master and slave cylinders and their O-rings fully loaded. Keeping things loaded wears them out faster than letting them unload.