Why is the use of alloca() not considered good practice?

Question

alloca() allocates memory on the stack rather than on the heap, as in the case of malloc(). So, when I return from the routine the memory is freed.

Answer 1

Old question but nobody mentioned that it should be replaced by variable length arrays.

char arr[size];

instead of

char *arr=alloca(size);

It's in the standard C99 and existed as compiler extension in many compilers.