That's only if the distro is recent enough; sooner or later, you'll encounter a box running a distro version from before /etc/os-release became the standard, and you'll have to look for the older distro-specific files like /etc/debian_version.
> you'll encounter a box running a distro version from before /etc/os-release became the standard
Do those boxes really still exist? Debian, which isn't really known to be the pinacle of bleeding edge, has had /etc/os-release since Debian 7, released in May 2013. RHEL 7, the oldest Red Hat still in extended support, also has it.
> the oldest Red Hat still in extended support, also has it.
You would be alarmed to know how long the long tail is. Are you going to run into many pre-RHEL 7 boxes? No. Depending on where you are in the industry, are you likely to run into some ancient RHEL boxes, perhaps even actual Red Hat (not Enterprise) Linux? Yeah, it happens.
