Question

Why we need to allow Users to Use Either the Keyboard or Mouse?

Answer 1

Because the different users have different habits, for the user interface, some users like using keyboard only, while other users like the mouse only, or someone even like switch between keyboard and mouse. In order to satisfy all the users habits for sure, the best solution is to enable both keyboard and mouse at same time and their operation can be the same but won't affect each other.

Answer 2

The keyboard and the mouse are computer peripherals. Using either one would interact with the computer. Some computers are accommodative and incorporates on-screen keyboards which may need the user to either tap or use the mouse depending on the type of computer that is used.

Interaction is important when collecting some sort of inputs (alphanumeric, numeric, letters/words, or special characters).

Many depend on the type of user interface that is given.