Because these warnings depend on optimization, the exact variables or elements for which there are warnings will depend on the precise optimization options and version of Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. is not smart enough to see all the reasons why the code might be correct despite appearing to have an error.

Reduce compilation time and make debugging produce the expected results. Lambdas are much more concise than other ways of defining function objects to be passed to STL algorithms, which can be a readability improvement. Here's one common (and broken) application of metaprogramming - the ultimate purpose is to be able to print arbitrary object at run time: // an abstract base class wrapping objects of arbitrary types. // there can be several such classes in one large project struct Obj { virtual void print(std::ostream&) const = 0; }; template struct ObjImpl: Obj { T wrapped; virtual void print(std::ostream& out) const { out < < wrapped; } }; // now we can wrap int objects with ObjImpl and string objects // with ObjImpl, store them in the same collection of Obj* // and print the entire collection using dynamic polymorphism: void print_them(const std::vector& objects) { for(int i=0; i< (int)objects.size(); ++i) { objects[i]->print(std::cout); // prints wrapped ints, strings, etc. std::cout < < std::endl; } } Typically there are 10 more layers of syntax involved, but you get the idea.