A channel is an entity in which you upload your videos. Creating several of them helps you to organize and separate your content.<x id="LINE_BREAK" ctype="lb" equiv-text="<br />"/> For example, you could decide to have a channel to publish your piano concerts, and another channel in which you publish your videos talking about ecology.
An HTTP request has to be sent on each tracker for each video to spy. If we want to spy all PeerTube's videos, we have to send as many requests as there are videos (so potentially a lot)