In my opinion Rhyming is ok in songwriting. You obviously don't have to rhyme, and your not going to get crucified if you do. Bob Dylan, one of the best songwritters in American history, rhymed every line he sung. And there are guys out there who don't rhyme and write exceptional lyrics. One good thing about rhyming is it makes that line particularly memorable and it gives it a nice hook. The best place to rhyme is at the chorus, or prechorus just for that fact. The verse is where you tell your story so rhyming too much there makes it cheesy. Not all rhymes are doctor suess rhymes, you can write intelligent catchy rhymes and really make a song baddarse. My 2 cents.