How helpful is your bank's (BB/EB) alumni network down the line?

I know people rely on their undergrad and MBA alumni networks all the time, but how helpful in your experience are people who worked at the same bank? Like if I were an analyst at MS or BAML or EVR would reaching out to people from my firm who are now in PE or wherever be helpful or is it best to stick to schools? Genuinely curious as to how much residual loyalty people take away from their analyst days.