system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we vocalize our thought process by saying, "um"?

Is there an actual reason behind this, or is it simply considered some form of a crutch for the way we communicate?
gpt
It's a mechanism for holding on to the conversation ball. By using discourse markers and vocalised pauses ('like' and 'y'know' vs 'er' etc) we indicate that we're still speaking and please would the other person wait until we're done. Essentially it's a way to indicate whose turn it is to talk, without losing our place.

It's noticeable that if we intentionally don't use them, unless our conversation partners are good at reading nonverbal cues we'll probably be interrupted more often in pauses.

One of the reasons people who don't use discourse markers sound 'smart' is because the only way to achieve that without constantly being interrupted is to think fast and keep talking. Refer to the BBC programme 'Just A Minute' for examples of that skill being demonstrated with punishment for failure.