When i started a long time ago it was general practice to include the seekbar/scrub-bar so learners would know how far they have progressed in the slide.
What is the current attitude/research on showing the seekbar on lessons of less than 10 minutes when there is narration on each slide?
I always lean toward more user control rather than less.
In general usability, I still refer to 10 Usability Heuristics for User Interface Design.
See:
#1: Visibility of system status
#3: User control and freedom
Hope that helps.
I agree with Scott and prefer more user control.
And on the accessibility side of things, it is worth the effort to follow WCAG 2.0 guidance, at a minimum, with a transcript available, and ideally closed captions.
