Here's an article (SPOILERS!) about the plotting problems created in Game of Thrones and other stories by an omniscient (all-knowing) character. I'm going to read it through again, but what I got from this was that it's just too tempting to the writer-- having this character who can see everything and know everything without ever having to work for it.
There are plot benefits to characters having to struggle to discover, learn, figure things out. The shortcut of using an omniscient character can cut short that process, and make almost automatic what ought to be earned by the characters.
It is tempting, however!
I would suggest that if we use omniscient or telepathic characters, we can make it more interesting by:
1) Creating a cost for the knowledge (like she gets terrible headaches or he loses a month of his life for each vision)
2) Making the knowledge less than obvious so the characters have to interpret it, and might interpret it wrongly.
Struggle is interesting!