This is exactly the time when you avoid all of the effects. Less is More and the emphasis is on getting your message/Story across without the distraction of too many Transitions.
Mostly the straight Dissolve, Page Wipe or Circle Transition with soft edge are used.
Unless it actually adds to the Story, then the images/narrative should speak for themselves, otherwise the viewer ends up wondering what trick the maker is going to perform next rather than concentrating on the message.
Jill