Ground is always there just for safety. It is supposed to be connected to any metal bits on the outside of any device, so that if a live wire touches the outside it just shorts and some fuse blows or circuit breaker trips, rather than providing an unpleasant surprise to anyone who touches it.

Most modern electronics is “double-insulated”, meaning there are at least two layers of reinforced insulating material between any mains-carrying conductors and the user. This is deemed to be safe enough so that those devices don’t need to be grounded, and if the case is plastic then they will almost never be. So if you’re only connecting plastic-cased electronics to the socket, a ground would be superfluous in almost all cases. There might be some exceptions, like power supplies connecting one of the low-voltage pins to ground, but it is quite rare to see.