You really deserve a straight answer lol. That panel does three things:
1) Yes, it keeps dust out and provides a clean look for the back of the case.
2) It provides a shield to minimize the radiation of "radio waves" that could theoretically cause interference with other devices, and
3) It ensures that each external connector - and therefore every device plugged into one of those ports - is connected to the SAME ground as the case. IOW, everyone's zero volts is actually the same "zero".
If you have any issues with any device plugged into the back - like a strange hum from your speakers - you really can make your own shield out of aluminum foil. Odds are you won't have any problem at all.