It’s unlikely that you will have to give an elevator pitch of your research at the viva. I’ve never heard of examiners asking for a polished thirty-second or two-minute overview of 3+ years of work.
But that said, exploring a concise summary could be a useful part of viva prep. You could:
- Highlight the most important points of your research;
- Organise your thinking about key ideas;
- Rehearse using technical terms and jargon;
- Practise talking about your work.
Your examiners don’t want a pre-prepared speech as a response in your viva, but rehearsing a pitch for your research could help how you think and talk on the day.
