The avi object will show playback controls, so you probably want to avoid video files for this reason only.
I hate cutscenes, I love manuals. O_o
Whenever a cutscene comes up, my mind goes "oh, I gotta stop playing and watch. I wonder how long it will keep me from playing". I really enjoy GTA's dialogue en-route to the mission location, you're still playing and you're also getting briefed, kinda like HL2's in-game cutscenes but better.
My take : Cutscenes are a holdover from movies, just like old movies had a holdover from books so they had a lot of text to read at the beginning and end. Movies got rid of that and we should get rid of cutscenes too.