To some extent you can predict the kind of topics that you might be asked to talk about in the IELTS interview. This means that it is quite common for interviewees to prepare answers in advance and learn them by heart. Then, in the interview if the topic comes up they will regurgitate (verb; repeat after memorisation) their answer – whether it answers the question or not. There are several problems with this approach.
Firstly, it is usually very clear that an answer has been memorised as it sounds very unnatural to the examiner. Examiners have a lot of experience interviewing people and they can easily see when something isn’t quite right. If they suspect that the answer has been memorised they will probably interrupt your answer and move on to another question.
Secondly, if you have memorised an answer it is very unlikely that it will actually answer the question directly and this will be another signal to the examiner that something isn’t quite right.
In summary, you should avoid trying to memorise answers, but you can still prepare for the interview by thinking about possible topics and making sure you have the vocabulary and language to talk about the topics in general.