A student wrote to me with a useful question:
"My IELTS teacher told us not to mention complex subjects and show off knowledge in the speaking test. I tend to talk about my major using big words and terms to expand my answers. Would this be seen as "showing off knowledge"? And what do you think about this advice?"
To answer this question, let's compare two answers to the question "how often do you eat chocolate?":
I probably eat something that contains chocolate, like a chocolate bar or a cake, every couple of days.
I try to keep my chocolate intake to a minimum because it is relatively high in calories, and because sugary foods can lead to insulin resistance.
The second answer might look more difficult and impressive, but it actually seems inappropriate and unnatural. I much prefer the first answer. So, I think this is what the teacher meant when he/she advised students not to "show off their knowledge", and I agree with this advice.