[ostensible]

I have switched to using xargs to parallelize things: it has a benefit of being part of posix, and is not annoying about citations like parallel.

[twic]

The parallelism isn't part of POSIX though (AFAIK), that's an extension by whoever wrote your xargs.

If what you really mean is that it's already installed on every machine you use, fair enough. But it's not strictly portable in some standards-based sense.