I understand; it's very hard to make every single line of a song meaningful and interesting. Only a few lyricists (like Cole Porter) could ever consistently manage it. I also don't mind metaphors and similes in lyrics, for they often serve a valuable purpose. That said, I frequently encounter lyrics in which metaphors and similes seem so fantastically pointless or out-of-place that one can only imagine that they were included as filler, a rickety bridge for moving the song from one idea to another.
To be sure, there are plenty of these to be found in flops, but (as is my wont) I prefer to use examples that everyone already knows. My first example is from Wicked, a musical that I do genuinely like. My affection for the show, however, does not extend to the chorus of "For Good." The song starts out strong, with a bittersweet reprise of the "Unlimited" interlude, and then an emotionally intimate moment in which two characters admit how much they mean to each other. And then the similes start.
Like a comet pulled from orbit
As it passes a sun,
Like a stream that meets a boulder
Halfway through the wood.
The problem with these similes is not the content but the context. Metaphors and similes are only useful in lyrics when they are able to express an idea or emotion that could not be adequately conveyed through a more direct method. The previous verse had already established, in refreshingly personal terms, the central emotional kernel of the song. The idea of a seemingly unalterable course being interrupted is a powerful but uncomplicated one that requires no embellishment beyond simple, emotional truth. Pulling the idea back into broad generalizations and repetitive examples serves only to tell the listener that it's safe to tune out; "there's nothing to see here."
A very different form of problematic comparison comes from Les Miserables. Again, I feel obliged to provide some small disclaimer to the effect that I do actually like the show. In fact, on the whole I even like the lyrics. At any rate, they are far better than a glorified translation has any right to be. However, I have always had a bone to pick with one particular line from "I Dreamed A Dream." The song, of course, is a classic tragic ballad that tells its story with unflinching clarity and naked emotion. At least, it does until it comes to one particular line:
But the tigers come at night
Were tiger attacks a big enough problem in nineteenth century France that they would be the first thing to spring to the mind of an impoverished factory worker? Wolves, maybe, but tigers? The next line only digs itself in deeper:
With their voices soft as thunder...
A line which makes you wonder, if nothing else, whether the lyricist is thinking of the same natural phenomenon we're thinking of when he uses the word "thunder." Or maybe thunder is really soft and my hearing is just too sensitive.
Again, there is absolutely nothing wrong with metaphor and simile, just so long as they have a good reason for being there, as long as they mean something. I care about Elphaba and Glinda, I care about Fantine. What I decidedly do not care about are comets, streams, and confused French tigers. Why bring them up?