for emails that span a lot of information to make sure all details are available to the recipient but also having enough awareness that it is not likely all going to be taken in at once by the recipient justifies the BLOT (summation).

BLOT is rarely something that someone that is unaware of their rambling puts in their own message. Which is likely why on Internet message boards you haven't seen it much - most don't realize that their ramblings are relatively useless to others. Likely because someone has then been challenged with TL;DR many times for their comments they start using it themselves thinking it is the correct way to preface or sum up their thoughts when really it started as a way to mock them...

I work as an IT Manager in a role where my team sits between the heavy techie people and the business leaders/end users. One of our primary roles is to bridge that communication gap between those that understand tech and those that understand business. Often our email hits both parties and members of my team often have struggled in the early going in this role including enough info but stating things in a way both sides will understand. I've had to have many performance conversations on their business communications in email format. BLOT was the most common and useful technique that expert business sources my company provides noted to help with the issue...