First you got to know how an Inductor works.
An Inductor prevents sudden change in Current.
Assume you have an inductor is series with a switch and to GND.
Now when switch(which is a switching device like a MOSFET) is closed, the current rises and attains a stable value across inductor, through switch and to GND.
Suddenly if the switch is now opened, then as we know the current cannot change in the inductor fast enough(due to its property), there is a high voltage generated across the Open terminals of the Switch(faradays Law). This voltage may become high enough to damage the switch.
To provide this current a route to flow, we hook up a snubber circuit.
To answer your question about why only inductive loads. It is because resistors do not block current from changing too fast, so no voltage is generated, so it does not have that issue.
Back EMF for Inductors: As the magnetic field in the inductor grows, it induces a current that works to counter the source battery generated current. It is said to be generating a BACK EMF, and it does so, till the current does not reach a steady value.
TO Protect it an inductor from damaging a switching device, we connect a snubber/protection circuit, allowing current to flow through it, thus preventing a high voltage across switching device.