Gotta disagree, Niteshift. It's just a tool, it works, and a free one at that. I, personally, would not use it so much to write a song from scratch, but it's handy for tweaking / perfecting a lyric. It gives you syllable count for each line and rhymes for each end rhyme. Cut and paste and see problem areas with syllable count. Get ideas for other end rhymes that could take the song to a better place, giving you a spark of an idea to take the story to a new place.

I do not write with rhyme book in hand but I do use one from time to time to stimulate ideas. Writing a lyric is easy. Writing a great lyric is another matter. My method is to write, write, write, sing, sing, sing, write, write, write, sing, sing, sing. Until it's as good as I can get it. And that does not happen in a couple of hours. For me. It takes many hours of work. A tool can help.