It doesn't, it only touches the drive you perform it on (meaning your Mac HD). I literally did a fresh install yesterday with an existing bootcamp partition, an

It doesn't, it only touches the drive you perform it on (meaning your Mac HD). I literally did a fresh install yesterday with an existing bootcamp partition, and no problems. One thing though, if you relied on some thing like Paragon or whatever to read your HFS drive, that will obviously not work anymore (not personally a problem, but could be a deal breaker for some).