I don't know. At first, I thought maybe it's just that you're overwriting values that it will perform later, but then I remember this scenario...
audio_sound_gain(snd,.5,1000); // will fade sound from 1 to .5
audio_sound_gain(snd,0,0);
audio_sound_gain(snd,.5,1000); // will fade sound from 0 to .5
So I would assume your commands will stack up and cost some amount of performance, but again, can't be much.