Often we have a heavily animated presentation, where each slide has custom
animation for its text and graphics. 

But often the presenter learns that he will not get enough time. 

Typical examples: 
(a) At a seminar, the earlier sessions take too long; and he has to finish in
the remaining time ("before lunch-break")

(b) At a business meeting, a senior person suddenly tells him that he/she has to
leave earlier; and could the presenter make his pitch in half the time?

Under the circumstances, the best that the presenter can do is to present the
slides without animation.

Impress should have a facility to suspend all custom-animation during a slide show.

Currently Impress can only stop the animated images (e.g. gif) from animating
during a slide show. This serves only a minor purpose: It suppresses an
animation that is distracting. 

On the other hand, stopping the custom-animation has a very serious business
implication for the presenter; something that can make or break his career.