|laziness, impatience, and hubris|
the format of the spoken presentation.
Even in a spoken presentation, repetition is just filler.
Some sources try to suggest that it is an application of Spaced Repetition, but this is proven wholly false. For spaced repetition to work, the facts have to be concise and discrete, and must be repeated verbatim. There has also been research that suggests that the timing of repetitions is an important factor in the benefit of repetition, and that the length of the average presentation is simply too short to usefully achieve the benefit of 3 repetitions; even if those repetitions were correctly structured and verbatim.
With the 'tell'em what you're gonna tell'em; then tell'em; then tell'em whaty've told'em.' meme, the pre & post summaries lack any useful details, so fail to serve as useful reinforcement. Indeed, it has been shown that the preamble serves to cause many of the audience to reach pre-conclusions about the usefulness of all or parts of the session; and/or start anticipating later elements of the talk thereby distracting them from digesting earlier parts that they've pre-concluded to be unimportant.
There is some merit in summarising a previous dependant session -- "Last time we explored how X led to Y; now we'll see how that helps us to achieve Z" -- but in all cases, written handouts are far more useful than filler summaries, because:
you don't have to repeat yourself to make a point because the reader can re-read.
It also leaves more time for looking at some of those details that are traditionally skipped because of "lack of time". Or, allows shorter presentations saving the delegates money; or enabling them to attend more sessions.
There really is very little merit in the "three Ts" beyond padding trainers saleries and training company coffers.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
In reply to Re^3: Introduction to Technical Writing/Documentation