It can do what ever the plot needs it to do.
End of debate.
I know that sounds harsh, but when you think about it, the writers came up with some pretty odd ways of using the deflector (something designed to push interstellar dust and such out of the way) to help the story along or end some sort of disaster.
Well, to its credit, the deflector IS a rather large focusing antenna array.
Given the technological abilities of Federation ships, one would surmise that channeling directed energy through the thing would be a piece of cake.
They've used other equipment in a rather 'unconventional' capacity.
My guess would be that SF designs their ships with ultimate versatility in mind - and while other systems could be used on separate occasions in a different capacity, its not exactly recommended to do it ALL the time (unless modified to support the function long term).