I find them very useful for testing codes, as a sort of rapid-response travis. I run a script that pulls any new modification into each of my five "pets" (open

I find them very useful for testing codes, as a sort of rapid-response travis. I run a script that pulls any new modification into each of my five "pets" (openbsd, slackware, freebsd, voidlinux+musl, dragonflybsd) and runs the tests. Since the systems are so different, it is very easy to break something. Since you notice it immediately (and not after waiting 1 minute for the travis answer) you develop a sense for avoiding non-portable things.