This method would function similarly to the Clear method of the ParticleEmitter class, clearing all the existing textures that have been emitted by the Trail object. This would save developers the hassle of making the Trail invisible and waiting for the textures to despawn.
For example, I have a laser sword that has a Trail effect turned on when the user swings it. However, when the swing is over and the Trail is disabled, the textures on the end stick around for a few extra 10nths of a second before they disappear, giving an undesirable visual effect.