An advantage would be, because TV is so globally accepted and cultivated, there is a lot of useful information you can learn, just by watching. The news, though often times it won't be extremely upbeat, will let the child know of other people living all over the world, more socially aware in a way and possibly inspired or taught a lesson by something they see. The Discovery Channel is great for learning all kinds of things, and has quite a few entertaining shows. Also, television can give children (or anybody really) an insight on how things work in other cultures, or even how the things that are out of their reach work (like chefs, doctors, fashion designers, etc.). Among other things, of course.
Disadvantages would be that there is also a lot of bad stuff on TV. Inappropriate, morally wrong to be seeing at a young age, provocative/sexual, inappropriate comedy, violence, swearing, over-dramatic everything, none of which are necessarily good for a child to be seeing. Also, if TV takes up too much of their life, they may start to act more and more like what they see on screen. It could also alter how they react to real life situations that they happened to see on TV.
I'm sure there are more things, but I hope this is a satisfying answer.
Disadvantages would be that there is also a lot of bad stuff on TV. Inappropriate, morally wrong to be seeing at a young age, provocative/sexual, inappropriate comedy, violence, swearing, over-dramatic everything, none of which are necessarily good for a child to be seeing. Also, if TV takes up too much of their life, they may start to act more and more like what they see on screen. It could also alter how they react to real life situations that they happened to see on TV.
I'm sure there are more things, but I hope this is a satisfying answer.