One way to look at it is this. Picture a (co)sine wave,
continuous in time, and pick a point anywhere along it. As you go
forward, conventionally its phasor rotates in an anticlockwise
direction but while going backward it rotates the other way.
One set of solutions to Maxwell's equations generates "advanced" waves that
all converge on the source, moving backwards in time.
Sounds extremely weird, but it's one possible explanation for the phenomenon
known as "radiation resistance", which IIRC the explanation of is usually
just glossed over.
Major, rational, mature, Nobel prize-winning physicists have theorized at
length about this, some have even set up experiments to scan the skies for
Basically you set up a microwave transmitting horn and wave it around the
sky while watching a very sensitive SWR meter for fluctuations. No such
variations found yet, but it may be due to the Universe being a lot more
homogeneous than expected.
Or do you mean the average MOTOS consortium rate of the average EE ?
For one thing, they are useful for explaining the lower sidebands that
appear during amplitude modulation. They are also useful in understanding
aliasing which often occurs when continuous signals are sampled and
converted to the discrete time domain.