It's not necessary per se, but many programmers do it out of good habits. It becomes much harder to e.g. find memory leaks in your code if you never free the me

It's not necessary per se, but many programmers do it out of good habits. It becomes much harder to e.g. find memory leaks in your code if you never free the memory you haven't leaked. And normally the extra overhead it entails is imperceptible. Obviously many programmers do not think to (or cannot easily) test their code with 40 TBs of data.