not showing off for English

talking about things related to the topic plainly

let people understand what you are mainly talking about

to make people feel'engrossed' and understand that what you are trying to say must be interesting

without Singlish, people will get to understand the plain words that you use because if we use Singlish in the speech they will think differently (Singlish is another language) so they will feel that they did not 'hear'/understand the rest of the speech which is Singlish

if we use this words but the topic isn't about English,people might think that speech is boring because if you use too much of these words,they will think that your speech is spoiling/affecting the topic and its like you are referring to another topic---English.

it is not really relevant to use these kind of words in a speech so that people will understand more about the topic you are introducing (unless it is in educational English for composition

so that the communication between you and audience verbally makes audience interested in the topic

contrasting public speaking and debate topic