> but renaming every integer seems senseless.

When the integer itself is self-explainatory but you can't just assign the integer as a name.

For example:

   constexpr int 42 = 42; // compiler error

So instead:

   constexpr int fourtytwo = 42; // yay!

However the obviousness of what 42 means is debatable.

   int universe = fourtytwo; // why?
   int sum = fourtytwo; // sum... of what?
   int magic = fourtytwo / 7;