No, you can choose:
- to have them parked and not redirected to your main domain name;
- to have them parked and redirect them to your domain name
To have a domain parked is technically when that domain is alive but not having a real site related. But it still has to have an html page.
That is why that parked domains and not parked domains has to allocated in different spaces. If not you would have them showing your main site, as a parking page (which is not anything else than an index.html) cannot coexist with the index of your site.
If the parked domains are allocated in separate spaces in your hosting (/domain-parked-1, /domain-parked-2...), then you can choose if redirect them or not.