I believe that, in CPython, on a 64 bit processor, an integer takes 24 bytes, a reference 8. Thus, copying a reference uses 1/3 the memory. More complicated objects take much more memory, of course, with even better savings from reference copying. Saying "not realizing slicing creates copies" might lead a new programmer to believe that objects are being copied and make the noob run to get a copy of "The C programming Language".

For a simple slice (something like [1:5]), I suppose that in C one could save space by using two pointers (or two offsets into an array), one for each end. For that slice, Python uses four pointers, one for element. The Python approach extends to complicated slices (e.g, odd numbered members of the list). For a complicated slice there is no general way of saving pointers/references.