You never need to use scripting. It's just that it can make certain things easier. First you have to know why you want to have scripting and what it should do. You also need to decide what scripting language you want to use or implement your own. Lua is seems to be quite popular. http://www.lua.org/
Games usually do use scripts, especially the big ones. Scripting is generally for upper level control though (Game Designers) and C and C++ (and maybe some Assembly) are lower level (Game Programmers).