If it is necessary to connect the keyboard and mouse, Android users can easily use a keyboard and mouse, this can be very useful. If your screen is damaged or if you just need to type a lot of text, then you will use OTG cable to attach Keyboard and mouse easily to Android Phone and do your work easily.
If your Android screen is damaged and not write a text, or you want to write a lot of text on it, then you will attach the keyboard to the Android phone. For this, you will require OTG cable or USB On-The-Go Cable. Using this simple technique you will be able to control keyboard connected to your Android phone and you will do your work easily.
If you want to connect a mouse to your Android, because your device is damaged or your touchpad is not working properly and you need a mouse to operate your Android Phone, then you will connect Mouse. Same procedure as above you will use OTG cable and using OTG cable you will easily connect a mouse to your Android phone and start your work like send important text messages, sending documents on email, all things are making easier.
So all this happens when you need it, otherwise not, use of this technology is optional or making to do something when resources are not available at that time then you will use it.