Developer, Former MVP, now at Microsoft - Best of 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013
Once a feature has shipped, it is very hard to eliminate it from the next release. If I was in charge of the PowerPoint product, I would not hesitate for a second to remove the dreadful AutoFit feature.
Fortunately, AutoFit can be turned off on a slide-by-slide basis and, even better, globally: go to the PowerPoint "Options" and under "Proofing" find the "AutoCorrect Options…" button which brings up the dialog where you need to uncheck the last two checkboxes (see the screenshot to the right).
AutoFit is the ability for the user to keep hitting the Enter key as they type more and more text into a slide and it magically still fits, by shrinking the space between the lines and then the text font size. It is the root of all slide evil. It encourages people to think of a slide as a Word document (which may be your goal, if you are presenting to execs in Microsoft, but that is a different story). AutoFit is the reason you fall asleep in presentations.
AutoFit causes too much text to appear on a slide which by extension causes the following:
In contrast, the absence of AutoFit
You could argue that everything above has nothing to do with the AutoFit feature and all to do with the advice to keep slide content short. You would be right, but the on-by-default AutoFit feature is the one that stops most people from seeing and embracing that truth.
In other words, the slides are the tool that aids the presenter in delivering their message, instead of the presenter being the tool that advances the slides which hold the message. To get there, embrace terse slides: the first step is to turn off this horrible feature (that was probably introduced due to the misuse of this tool within Microsoft). The next steps are described on my next post.