As others have said, this does justice to the idea of actually learning a new language...or perhaps because it is Racket a new family or ecosystem of languages. Anyway, if you're still curious about pairs verus lists and why anyone would use dotted pairs, I like to think about it as where Lisps show that they are from the age when running close to the metal was a given.
And it all goes back to car and cdr and the fact that they are (or rather were) embedded assembly language and there to give raw access to Lisp's linked memory model (as opposed to the sequential memory model of Fortran). A dotted pair has two efficiency advantages over a proper list and both stem from the fact that the last cell of the last pair of a proper list contains 'nil (or 'null in Racket).
Storing two values in a proper list requires two cons cells - the first with the first value and a pointer to the second cons cell and a second cons cell containing the second value and a null pointer. In contrast, a dotted pair holds two values in a single cons cell - halving the memory requirement.
The second advantage is that when there are only two values there's no need to walk the list and test for 'null (or 'nil) on the cdr. This saves an instruction step.
Philosophically, dotted pairs allow for car and cdr to be used symmetrically. Calling cdr on a dotted pair returns the second value directly just as calling car on any list returns the first value directly. Lastly, one of the things that is awesome about Lisp is the way in which lists can model data structures, and in the case of a dotted pairs their efficiencies are available to all those structures which consist of or rely on paired values.
Of course, this may be obvious and on a machine with 10+ GB of RAM not really applicable, but I find it fun to think about anyway.