The default for many programs which output a hexadecimal dump of data is often 16 columns of octets. Defaults for binary or octal dumps are often different, but usually something similar to that width.
However, that could be awkward for users on mobile devices with narrow displays. Add the offsets and the US-ASCII rendition on either side, and it can be quite wide in a monospaced font — especially if you separate each octet for better visibility.
If there isn't a recommended maximum width for GameDev Stack Exchange, then perhaps it should be discussed here.
I ask this here rather than on the mother of all metas because I think the needs of different sites would have some bearing on this. (Also, I think that the aforementioned site is a disaster that should be avoided like the plague, but whatever.)