First off, I'd just like to say that I don't really watch that much
TV anymore. The only shows I do watch are:
Buffy the Vampire Slayer,
Angel, and
The Simpsons (and the occasional program on
The Discovery Channel). However, I am still of the opinion that television can be a Good Thing
TM.
How TV can be good:
I: Continuing story development
Television offers a medium that allows for the continued development of characters and plot lines over several years, depending on the length of the series. This provides the shows creators and writers with an excellent way to advance their story over time, in ways that aren't possible, with movies or books. Examples: Buffy the Vampire Slayer, Babylon 5.
II: Educational programming
TV can be used to disperse educational material, such as video and audio that would not be available in textbooks, and is also more easily updated when new material is made available. TV can also be broadcast live, or retransmitted from lectures, or actual field sites. Examples: Carl Sagan's Cosmos, or educational shows on The Discovery Channel or TLC (excluding things like Junkyard Wars).
III: News (live coverage)
Television can bring news and information to a mass audience. Especially in the area of live coverage of current events TV provides a medium to bring news to people around the world. Example: September 11, 2001: CNN.com - Down, CNN Channel 25 (where I live) working perfectly.
I'm sure there are more reasons than this, but keep in mind that TV is just a medium, just a way to convey information. It is neither good nor bad by itself, and should not be judged as a whole. There are some good things on television, and there are some not so good things, but you could say the same about the Internet.