FreeBSD's /bin/sh is based on ash, like NetBSD's, although I'm not sure how much they have in common these days. dash was forked from NetBSD's version of ash a

FreeBSD's /bin/sh is based on ash, like NetBSD's, although I'm not sure how much they have in common these days. dash was forked from NetBSD's version of ash and then simplified considerably and fixed up to be fully (? or at least mostly) POSIX compliant. A while after that NetBSD's shell also had a bunch of POSIX fixes. I'm not sure how FreeBSD's shell is in terms of strict POSIX compliance. In my opinion, bash has two things (at least vs NetBSD's shell, possibly a few more vs POSIX) that make the average shell script (that I write) much easier. The first is &> which makes it easy to redirect both stdout and stderr to a file for logging. The standard 2>&1 can work but needs to be placed correctly or it doesn't work. That place isn't always the obvious place like it is with &> and running bash seems much preferrable to me than figuring that one out. The second is ${var@Q} which prints var quoted for the shell, which is nice to use all over the place to make sure any printed file names can be copied and pasted. My sense is that targeting POSIX is usually done for maximum portability or for use on systems that don't have bash installed by default. However, bash is quite widely available even if not by default and very widely used so I wouldn't say it is unreasonable to look at bash as the de facto standard and POSIX and other shells as being used in more limited circumstances.