Mentioned here: https://discussions.apple.com/docs/DOC-5521
I was just curious if this would really work. It makes sense to me. As long as they don't do reverse forensics on the bits on the hard drive... But does that happen often?
In case of an Apple site, the probable reason behind that they suggest a lot of small files, that they have fear from filling the disk with a large, single one. But, if you want to make sure without block-level overwrite, this is what you had to do. On any unix system, incl. OSX, there is a command
dd command for that, but there are also a lot of disk wiping tools for that.
In case of SSD: the disk sectors of an SSD disk can be overwritten only 10000 - 100000 times, after that they will die. The SSD controlling electronics has an internal reindexing mechanism to balance this load (some sectors are overwritten many times, these are re-mapped through the disk sectors). This is the wear leveling, and this will be overloaded if you overwrite the whole disk with random data on the sector level. Essentially, all of your data blocks get a single hit of overwriting. But a whole-drive wiping is not an everyday thing in the life of an SSD disk, doing this once is yet negligible harm, but it is better to know.
You can find some relatively sure ways to wipe the disk here.
On my opinion, a common "mortal" never meets technologies or organizations capable and willing to do such low-level data recovery techniques. Thus, the many question cycling on the about this is grounded mainly on the serious over-estimating the real threats.
For example, if you are a commoner trying to wipe a hard disk before selling it, a simple reformat will be enough. If it contains your very sensitive data, then wipe it with a specific tool. Even the forensics won't (be able to) go deeper.