matrices – Matrixes whose elements are matrixes

I’ve worked with matrixes whose elements are objects in a field, such that real numbers, complex numbers, inclusive functions in space of functions, but… Today I was talking to a friend and he asked me about something he saw in his PhD in informatic science that was about “matrixes with matrixes in their entries” and I know that we can make an arrange of the blocks of the matrixes in the entries to form a matrix in a nxn space, for some n… but… what use or there is any example of how is useful a matrix with this characteristic?