It's actually an article of faith among some here that having your content available to download for free doesn't in any way affect your sales negatively, an argument frequently used as a justification for mass copyright infringement.
So sales are affected negatively by free legal streaming, though under 10%. No surprise; I actually might have thought the lost sales would be substantially higher.
But the illegal download argument is different (note that I don't claim that copyright infringement is acceptable). Illegal downloaders likely wouldn't buy the content anyhow, so the lost sales would seemingly be small or even negligible.