What happens if the current is too low?
If the current is too low, the contacts won’t get cleaned and the switch might eventually become unreliable. Some switches are designed with dual current ratings—the contacts are gold plated to work reliably at low currents, but are big enough to handle high currents as well.
What happens if you exceed a components recommended voltage?
Voltage that is too high can cause premature failure of electrical and electronic components (e.g. circuit boards) due to overheating. The damage caused by overheating is cumulative and irreversible. Motors can, on the other hand, often benefit from voltages that tend to be a little bit high.
Is it OK to supply more current than its rated value?
To answer the title of your question, the answer is no. It is not ok to supply more current to a component than its rated value. However, it is ok to have a voltage power supply rated for more current than the components rated value because the component will draw as much as it needs.
Is it better to run a motor at higher or lower voltage?
Operating a motor at a voltage below nominal generally has no detrimental effect on performance. In fact, running a motor at lower than nominal voltage (and, therefore, slower than nominal speed) can result in less brush and commutator wear (for brushed motors), lower current consumption, and longer motor life.
Is it OK to supply more current than what the voltage is?
It does not matter if the power supply you are using to generate the supplied 5V is capable of supplying 0.05A or 5A of current; because the voltage and resistance are fixed, the current through the circuit will also be fixed.
How can I lower the voltage of a circuit?
There are a number of ways in which circuits requiring a relatively fixed supply voltage can be made to work relatively efficiently from sources having a wide range of voltage outputs. The simple, but inefficient way, is to use a simple series regulator to lower the supply voltage to whatever lower fixed voltage is required by the circuit.