Comment by malomn

Your question is very broad. Being a PhD student, I can only say that fine-tuning happens all the time. Research in particular areas require fine-tuning pre-trained models on specific tasks, taking advantage of the amount of data seen during pre-training. It's unlikely that your thesis will be solely about fine-tuning. However, chances are you will fine-tune many models during your thesis, for various tasks depending on your field of research.