One of the most important reasons to use calloc, other than the zeroing of the allocated memory, is the fact that it checks for integer overflows (at least on most implementations).

For example, when allocating an array of n elements, in malloc you would do something like the following:

ptr = malloc(sizeof(int) * n);

Which could potentially lead to an overflow of the size passed to malloc, hence allocating a significantly smaller buffer and end up accessing adjacent memory which hasn't been allocated to the buffer (buffer overflow)

Calloc requires two arguments, one for size and one for number of elements, which allows it to check for an overflow before performing an allocation (e.g. by using SIZE_MAX):

ptr = calloc(n, sizeof(int));

This is not to say that zeroing memory is not useful. There are many situations in which a zero in a memory block represents the end of the usable data, as for example in a string, so zeroing memory in those situations is definitely recommended.