There are programs that play audio for a short time (like notifications) and you can't change it's volume in the program and the sound is so short when you open the applet it's no longer there so you can't change the program's volume. Other use case is when you launch a program or game for the first time it can be really loud this would allow you to lower the volume before it starts to play it. I don't know if it's even possible but I hope it is.
This is not really feasible, sorry.