The earliest mention of OTM as an OASIS file specification that I could find, is from a discussion list in May of 2005, specifically, https://lists.oasis-open.org/archives/office/200505/msg00006.html
The only announcement of inclusion of OTM in LibreOffice that I could find, was a blog post by Caolán McNamara in September of 2014, stating that it was new for LibreOffice 4.4 --- https://caolanm.blogspot.com/2014/09/.
A message in 2015 briefly describes the background of why the OTM document file format exists. https://lists.oasis-open.org/archives/office/201502/msg00022.html.
In the help files of LibreOffice 6.3, there is a mention of it, as filter. CF https://help.libreoffice.org/6.3/en-US/text/shared/guide/convertfilters.html?DbPAR=SHARED
In theory, this file format will enable one to create sets of documents that share the same data, without having to go through the hassle of creating a new master document for each specific scenario, and hoping that one remembers where all of the shared documents, images, and the like reside.
In practice, I don't know. I've been struggling to create my first OTM document, with very little to show for it.
