That's the thing though, you have to remember filenames. I don't have to remember anything, just journalctl, because it can be run without any arguments and get logs for -everything that's running- including units I totally forgot about!
More than once I've forgotten the name of some unit I wrote -- the same as I easily forget filenames for random services I've installed, and where I might have installed them. I can discover the service name by calling systemctl status, or I can just call journalctl with no arguments and pass directly to grep to find what I need, in whatever unit it's in.
Try that when you have log files scattered all around your filesystem.
I concede it's as easy if you're just reading one log from one machine, but what if you're harvesting and/or merging multiple logs from multiple machines? It's much easier to do with simple unix tools and plaintext logs.
More than once I've forgotten the name of some unit I wrote -- the same as I easily forget filenames for random services I've installed, and where I might have installed them. I can discover the service name by calling systemctl status, or I can just call journalctl with no arguments and pass directly to grep to find what I need, in whatever unit it's in.
Try that when you have log files scattered all around your filesystem.