Preview responses are recorded in your data as a way to let you see what your response data might look like on the backend. 
If you don't want those responses to get captured, then while building survey you have to add below branch logic before every termination logic of your survey. Where, the end of survey is customized and "Do not record response" is checked.

The way you've described this, I feel like "preview" is being treated as a survey pilot - a distinction the product doesn't make.
Why not support a true "preview" case, where the point is to review the questions and the flow?

You are completely right Kathryn, I have the exact same problem and it is incredibly frustrating and anti-intuitive. I just want to test my survey; I shouldn't have to create a copy of it and then remove the de-duplication, and it shouldn't record the responses of the person who is building the survey.
I can't fathom why anyone would think this was intuitive or useful.

Just wanted to jump in here and say that you can easily remove specific responses from your dataset (e.g., deleting all preview or generated test responses) within the Data & Analysis tab. Check out this support page for more information, and if you have any issues, be sure to reach out to our Support team!

Hi Lauren,
Thanks for your response - I actually mentioned deleting undesired responses in my original post!
I'm interested in splitting previews and pilots in the product (see follow up to rondev's response), as opposed to the workarounds you both suggested.
Please let me know if there are any UXers or PMs I can provide more detail to, as this one of the things that irks me most when using Qualtrics.
Kathryn

Hi Kathryn! If you would like, you can post this as a new idea within our Product Ideas category right here on community! Our PM team now looks to the Product Ideas category when considering future product enhancements!

I just had to delete a dozen Preview responses. Deletion was oddly slow and cumbersome; it took a long time and I had to delete each preview individually. I had assumed Preview meant results would not be tallied. Otherwise, why is it preview? There should definitely be an option to have a preview not logged.

https://www.qualtrics.com/community/discussion/comment/30224#Comment_30224We can delete survey preview response all at once by adding filter on survey meta data -> response type-> survey preview