What's the significance of negative indices in python?

I was wondering why negative indices in python are so
important - are there any applications? I could just use

my_list[len(my_list) -
            1]

to find
the last element of my_list. Why do we need

class="lang-py
prettyprint-override">my_list[-1]


To
find the last element?

EDIT:
It's not
that I don't understand what my_list[-1] means, I want to know
where this might be used.