How to draw using reference - clip studio
Using reference is one of the best ways to improve your art, It would say you should never draw without reference, especially at a beginner or intermediate level. Only when you are professional you'll have the experience and the skills to draw from memory in great detail, but even then you'll probably want keep using them as they make your work look more professional.
Most professional artists, if not all, use references and I think it's the main thing holding beginner and intermediate artist back. I used to come up with poses and characters, but since I started using reference I improved so much.