Shadow and light!
Modern motorcycles have increasingly complex electrical systems: they need to power performance lighting systems, heated hand grips, alarm, radio, sockets for heated clothing and even a passenger intercom.
So, there is high draw on the battery, especially during repeated urban driving, over short distances during which the alternator does not have the time to recharge the battery.
The fuses act as a safety switch in case of an overload on an electrical circuit.
On the other hand, when fitting different accessories, this may mean that the power draw required is too high in relation to the motorcycle's capacities
The spark plugs
The ignition and spark plugs are also a part of your motorcycle's electrical system. On some models, the ignition module burns out; this is an expensive component, to be claimed under warranty wherever possible.
The spark plugs should not pose problems, unless there has been a drastic (and forbidden) modification to the carburation set-up and the exhaust on your motorcycle.