There are many things you never notice about the way you speak, but I do.
Let me introduce one of them.
One is the use of “and.” Here is part of a sample response to Q3 of 6 in the TOEFL Speaking Section.
The university is announcing a new ban on smoking.
And students will not be allowed to smoke in the dorm.
And if you smoke, you may be punished.
And the woman makes complaints about the new policy.
And she thinks drug problems are much more imminent …
That’s about it. Obviously, this sample uses too many ands. Its usage is irrelevant. This may be just a habit that the speaker has developed before s/he realizes. However, if you imagine listening to this response, “and” will be haunting you when it is time to judge this response. The effect will be negative.
I can assume that this habit comes from a strong desire of the speaker not to stop speaking. S/he wants to speak, but cannot say anything. That’s when “and” pops up. However, “and” should connect two sentences logically, the former sentence being a reason or an assumption, the latter a result or a conclusion. Or both have a parallel relationship.
I don’t think “and” can work as a filler. I would make a pause if I have to think before speaking. Just a pause of a second or two will not affect your entire speech.