What makes a cloned voice unusable for your project?

I'm on the FreeVoiceClone team, and I'd like to understand what creators need beyond a voice that sounds similar in a short demo.

When using your own voice, or a voice you have permission to use, what makes you stop and re-record instead? Is it pronunciation of names, flat delivery, awkward pauses, or the voice changing across longer passages?

For a tutorial, product demo, or translated video, which one would you fix first? A language and a short description of the issue would be helpful; no need to upload anyone's voice recording.

What would a usable result sound like for your next project?