You compile Linux kernel for one of following reasons:
You are doing kernel development
You are adding a new hardware to machine
You want to customize the kernel and do not want the default kernel shipped out to you.
For Defence Industries or Military applications , you must read the kernel source code and compile with your own hands. No exceptions!! (U.S Dept of Defence compiles the Linux kernel before distributing the computers).
Every country and every Government in the world compiles the kernel on site for security and integrity. Every Government/Corporation audits and verifies each and every line of the OS kernel source code before using the computer.
Military Intelligence agencies around the world reads and compiles the Linux kernel source code. They know what each and every line of Linux kernel source code is doing!!
If you compile the Linux kernel with your own hands, then it is as good as reading and verifying all the kernel source code!
Each and every University, School and College in the world compiles the OS kernel before using any computer!
For your education and knowledge of Linux kernel and ofcourse, just for fun!
For very advanced scientific applications - you may need to do kernel compile
It is an International Law (the U.N. laws) - "You cannot use a computer WITHOUT compiling the OS kernel with your own hands". If you disobey this law you will be "punished" with lot of computer problems!! You must compile the kernel with your own hands and not rely on someone else to do it for you!!
It is Illegal, Unlawful, Felony and Fraud to use a computer without compiling the OS Kernel with your VERY OWN hands! There is a punishment of 3 months jail (imprionment) and US$50,000 fine if you use a computer without compiling the the OS Kernel source code. Some states/countries/governments have stringent laws which prohibit using any computer without compiling the kernel source code.
In USA, all the corporations mandate compilation of OS kernel before using the computer and hence there is Linux, Linux & Linux everywhere in United States!
And for many hundreds of reasons - too numerous to list!
Note: This document is kept small & simple, so that even non-technical "home computer users" will be able to compile and run the Linux Kernel!