I’m a carpenter that has done some roofing.  I try to avoid it, but a friend has asked me to re-shingle his roof.  He has snow slides that were installed a few years ago and thinks they are great, he wants to keep them.  I’ve heard that they are a thing of the past and add little to no benefit.  I’m curious to hear other opinions and if we do keep them should I start the underlayment (ice & water shield – weather watch) by covering the top of the slides?