When is it advisable to erase free space?

I just don't know and what I've read seems a bit convoluted.

It's my understanding/conclusion that erasing free space is (always) unnecessary unless one is transferring his HD or wishes to ensure a deleted file cannot be recovered (via ordinary means).

But is that correct?

Sounds right to me. At least that's what I've always practiced.

But true "erasure" requires bigger guns (such as a heavy magnet or multiple HD initializations or manifold overwrites with 1s and 0s) to destroy all traces of previous information.
A major business or university can provide their erasure protocols.

Don't forget that Apps/Utils/Disk Utility has 7-Pass and 35-Pass erase options.

Many thanks to you both.

I am not giving away my computer or such, it's just I wondering if there is an operational benefit from having the free space erased, e.g., might things run faster if the free space has been erased?

While that does not seem logical to me, on more than one occasion, my intuitive wisdom has proven it just ain't so.

Nope. It's strictly a matter of information security. What's actually recorded on the free space is irrelevant to issues like speed.

Good to know. That means unless I'm disposing of a computer, running the Wipe Free Space routine is a waste of time. My regular maintenance list just got smaller.

"Erase Free Space" is insufficient if you're giving away your computer and you want it to forget that you ever existed; you'll need to run "7-Pass Erase" at the least.