About a year ago I set all of my music to be free to download. I've seen some interesting things happen. And while I can't say how this would reflect on artist who might have a bigger following than my meager half-a-handful, I can say I have seen a humongous percentage increase in activity.
Prior to 2014, I averaged roughly 0.2 play per month (according to my bandcamp stats). Around mid 2014 I set all my music for free. From that point onward I have seen a steady increase in activity in my plays with an interesting peak in October of that year (apparently my track, "It Has to Happen!" was really popular).
For a short period my activity from fans tapered off because I, myself, had become less active in producing. However, very recently, I began setting my signature that you seen here on KVR the same on other forums (except the link on the other forums actually goes to my 2014 album instead of my 2015 because I found many people would listen to the first track - which isn't actually a song - and then leave my page) and even when I am no where near as active on those forums as I am here - not that I am that active here any more either - I have seen about 5 to 10 plays per day, with a couple odd days where I got 20 plays (these must have been days that I actually made posts on those forums)
It's funny that a link that entices free music is more interesting on non-music related forums than it is on a music related forums. I guess that's because music composition and production become part of the mundane here, while on other forums it is a bit more....hmmm...I guess "abstract", or interesting.
Funnily enough, I have gotten hardly any clicks on my signature here on KVR
Overall, the "free" part of my music, I believe, sets a lower barrier to entry for those interested, and since there is no cost, it's easier to give some time to listen to the music to consider downloading or not. While my downloads are too few to really say if the free part has made much of a difference, there is a correlation between activity on my Bandcamp and the dates since whence my music went free.
Just some food for thought