On the other hand, when skimming some code, does it matter on the first pass whether a given variable is mutable? Probably not if we're just trying to get an idea of how it works; later on a closer read we can look closer if it matters.
If a variable is const-declared, I react in exactly the same way and know that I don't have to look for further uses, which I find very valuable.
I even do stuff like this, which might be extreme but I find it coherent and nice:
void * allocate_and_fill(size_t size, unsigned char x)
{
void * const p = malloc(size);
if (p != NULL)
memset(p, x, size);
return p;
}