Question

why the multiplexing is used

Answer 1

The very purpose of Multiplexing is clearly understood in its definition only - Multiple analog signals or digital data streams are ‘combined into one signal’ over a shared medium. i.e To reduce the number of electrical connections/Wireless Channels for transmission of several signals. 
Hence, reducing the number of individually independent interconnections.
It also simplifies the drive electronics, reduces the cost and provides direct interface with the microprocessors. The aim is to share an expensive resource.

For example: In telecommunications, several phone calls may be transferred using one wire. Else, you can imagine what would be the scenario if it wasn’t there.
Another Example: Your Cable TV receives all the channels over a Single Wire only because of Multiplexing only. Else,(Without Mux) You’d need a separate wire for each Channel OR worse than that!

Answer 2

Hey buddy here is your answer,

Multiplexing is a popular networking technique that integrates multiple analog and digital signals into a signal transmitted over a shared medium.Multiplexers and de-multiplexers areused to convert multiple signals into one signal.In telecommunications and computer networks, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource. For example, in telecommunications, several telephone callsmay be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910.

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