Smurfing is purposely lowering your rank. A sub account for practicing new things/heros isn't smurfing and there's nothing wrong with it if that's what you want to do.
On that note, as long as you start smurfing in placement matches, w/l records don't matter, so i have no problem with it. It's the people that purposely throw games just to lower their rank after placements that I can't stand.