It will delete {count, plural, =1 {1 video} other {<x id="count"/> videos}} uploaded in this channel, and you will not be able to create another channel or account with the same name (<x id="PH" equiv-text="videoChannel.name"/>)!
However, you may want to read <x id="START_LINK" ctype="x-a" equiv-text="<a class="link-orange" target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/admin-configuration?id=transcoding">"/>our guidelines<x id="CLOSE_LINK" ctype="x-a" equiv-text="</a>"/> before tweaking the following values.