@Dylan1 I have accepted guests with no reviews- it depends on how they communicate with me. Actually the same goes for guests with reviews. If they ignore any questions I might pose, or communicate poorly, I would decline. For guests with no reviews you might want to really make sure they have read the listing info thoroughly, house rules, etc.
If you decline a lot of requests, Airbnb will send you a warning and might even suspend your listing if there's a quite high percentage, so if you can get a guest to withdraw the request, you won't have to decline.
But declining is better than simply not clicking on either accept or decline before the click runs out, as Emilia explained. The first affects your Acceptance rate, which isn't even a criteria for Superhost, the latter affects your Response rate, which is.
And in case you aren't aware, if it's an Inquiry, as opposed to a Request, you don't have to either pre-approve or decline- just messaging back within 24 hours keeps your stats from being affected.