No respect for anyone who does it. Ruins the game. If you have a smurf to play with friends, then play normals. If you have a smurf because you can't do well enough in your own league and you need to stomp lower leagues, then I hope you're happy ruining the games for others.
Nothing creates more salt than losing a RANKED game and at the end, the most fed player on the enemy team says that they're smurfing. I thought they were good, but now I just think they're jerks.