I like vectors a lot. They're nifty and fast. But I know this thing called a valarray exists. Why would I use a valarray instead of a vector? I know valarrays have some syntactic sugar, but other than that, when are they useful?
Valarrays (value arrays) are intended to bring some of the speed of Fortran to C++. You wouldn't make a valarray of pointers so the compiler can make assumptions about the code and optimise it better. (The main reason that Fortran is so fast is that there is no pointer type so there can be no pointer aliasing.)
Valarrays also have classes which allow you to slice them up in a reasonably easy way although that part of the standard could use a bit more work. Resizing them is destructive and they lack iterators they have iterators since C++11.
So, if it's numbers you are working with and convenience isn't all that important use valarrays. Otherwise, vectors are just a lot more convenient.