The "bad things" or "flakiness" referred to include crashing, instability, failure to boot, etc.

The LEM article that Quadraman refers to is consistent with what I'd heard: Install the OS in a sub-8GB partition, or else you will be sorry. Initially all would be well if you installed the OS in a larger partition, but as soon as any important system resource (e.g., extension, etc.) got stored beyond that 8GB boundary, the bad, flaky things would come out to bite you. The precise nature of the badness would depend on what got written beyond the boundary.