Transaction log size debugging

Would it be possible for someone more knowledgable to add a summary of
"Finding the size of your transaction log" to
https://wiki.postgresql.org/wiki/Disk_Usage ? I'm new to postgre, and had a
non-trivial debugging session of why our server had low disk space. It
turned out to be a logical replication slot that was no longer in use;
Resulting in a slow growth of the transaction logs that had to hang around.
A note on that wiki page (even just to the effect of "Here's another thing
than can take up disk space") would have been helpful in debugging.

Thanks!
-Ted Hahn