When applied widely throughout a system, this leads to the internationalisation of log messages. Thus lessening the anglocentric bias in systems software. Windows has done this for years, at least with its own system logging (other applications can still put free-form text into the event logs if they wish.)
About what you put in the log message: You can also put different fields in a line of text. Not getting the advantage or trade-off here.
About the internationalisations: As non-English developers we force all our systems who have logging internationalisation to English system language so we have a common ground for the messages. Understanding the English message is nearly no burden. Log Messages are Event triggers, either in code or in a developer's/admin's mind. If I get a log message in my native language I don't know which event that triggers, which makes it actually harder.
Really. I don't know any non-English person who considers log internationalisation a good thing. Fighting anglocentricism is a very anglocentric topic. Outside of UK/US that's a non topic. We (non-English people) are happy that there is a language we can use to talk to each other and we don't really care how it came to be that widely known.
And even if you don't speak English, I don't see the advantage of parsing \x03 instead of "Error:.*". Both are strings that have a meaning which is rather independent of its encoding.
journalctl --since="$(date -d'last friday 2am' '+%F %X')" --until="$(date -d'last friday 2am + 10 hours' '+%F %X')"
Now I'm no systemd apologist but maybe some of the hate towards systemd, journald and pals is unwarranted. If one gives these newer tools a chance, they actually have some nice features. Despite the Internet's opinion, seems like they were not actually created to make Linux users' lives difficult.
If binary logs turn out to be the wrong technological decision, I'm sure we'll figure that out and change over to text logs again. All it would take is a few key savvy users losing their logs to journald corruption and the change in the wider "ecosystem" would be made. But if all goes well... then what's to complain about? :-D
The example with the timestamps is also strange. No matter how you store the timestamps, parsing a humanly reasonable query like "give me 10 hours starting from last Friday 2am" to an actual filter is a complex problem. The problem is complex no matter how you store your timestamp. You can choose to do the complexity before and create complex index structures. You can choose to have complex algorithms to parse simple timestamps in binary or text form, you can build complex regexes. But something needs to be complex, because the problem space is. Just being binary doesn't help you.
And that's really the point here, isn't it? Just being binary in itself is not an advantage. It doesn't even mean by itself that it will save disk space. But text in itself is an advantage, always, because text can be read by humans without help (and in some instances without any training or IT education), binary not.
Yesterday I was thinking there might be something about binary logs. Now I'm convinced there isn't. The only disadvantage seems to be that you also lose disk space if you store it in clear text. But disk space isn't an issue in most situations (and in many situations where it is an issue you might have resources and tools at hand to handle that as well) It is added complexity for no real advantage. Thanks for clearing that up.