We have at least one of these (sy-fy).
There are problems with this:
- TV programs almost never run on a single channel. In some cases, they don't even run on a single channel within a single country. There's no room to add a tag for each channel that a program runs on, even if that was a good idea.
- There are many ways to view TV programs. Via a TV channel is one, but there's also downloading/streaming (e.g. Netflix, iTunes, Amazon) and optical media (DVD, Blu-ray).
- The tag tells you nothing about the question (unless the question is specifically about that channel, not just about a program that aired on that channel).
- The tag won't be consistently applied. For it to be of use, it would need to be added to every question that is about a show that aired on that channel - this requires very localised knowledge (or research).
- If the channel specialises in science-fiction/fantasy content (I gather this is the case with SyFy) then it seems likely that a vast majority of the TV series questions will get this tag; that makes the tag considerably less worthwhile (and it bumps useful tags out of the primary position).
On the other hand, I see no benefits in these tags. Would someone really want to follow questions about shows that happened to air on a particular channel? (Perhaps this is actually possible in some countries; it's certainly not in others). Would someone want to 'ignore' these questions?