The Garbage Words you talk of are a mixture of Discourse Markers and fillers.
Discourse Markers, like 'well', 'you know', 'I mean' are words we use in speech to separate different pieces of information. They are not really necessary for understanding but they do provide the speaker with a moment to collect his/her thoughts and organise them.
Fillers, like 'umm', 'err', 'ahh, are utterances that, as the name suggests, fill in gaps while the speaker thinks of what to say next or organise his/her thoughts. Unlike Discourse Markers, Fillers do not have any semantic quality.
Neither of these are essential for communication - note that they would not be included in written language - and do more for the speaker than the listener. In fact, a person who uses them extensively would very likely be subject to some negative assumption about intelligence or education - professional speakers often take courses to reduce their usage of fillers and vague discourse markers.
They are best avoided both to improve the speaker's image and to maximise the strength of the speech. If one is trying to be persuasive, he will not be as successful if the ideas are heavily punctuated with fillers and discourse markers as it sounds weaker and less confident; a well rehearsed and concisely delivered speech represents confidence and belief in the speaker's own words. Without that, the audience will doubt the speaker.
Hope that helps.