The Num Lock key exists because earlier 84-key keyboards did not have arrows separate from the numeric keypad. Num Lock would be used to choose between the two functions. On some laptop computers, Num Lock keys are used to convert part of the main keyboard to act as a (slightly skewed) numeric keypad rather than letters.
Since most modern desktop computers have a full-size keyboard with both a numpad and separate arrow keys, Num Lock is rarely used for its original purpose, and ends up confusing the user if the computer has for some reason activated or deactivated the Num Lock key without the user being aware of it. This is less of an issue on most laptop computers, since activating the Num Lock function typically requires use of the Fn Key; however, if a full-size keyboard is plugged into a laptop keyboard, then the Num Lock function is normally off, and the user would have to activate the Num Lock function to use the numeric keypad for numeric entry.
Keys affected by NumLock;
You can disable it from the keyboard, but if it's enabled in the BIOS, it will be back on at next start/reboot.
Hope this answers your question.