Yes ive seen IT. there are exceptions of course, but people normally don't want to watch real life conversations. If the actor stutters or stumbles, the director will probably say: "Take 243, stop fucking this shit up!". The protagonist or powerful character needs to sound enjoyable, confident and sympathetic. The audience wants to watch a movie where every word is understood. Throwing in a few stumbled words, or someone correcting themselves can add in a few seconds each time. TV shows more than movies have a time constraint they have to meet for each episode