I voted Almost Never as most of the players I've encountered simply don't care to add anything to the world. They wish to show up with a character they have put limited thought into and engage with the world on a limited level. At least, that's with most D&D only, player only types I've encountered. In systems other than D&D I find the level of engagement goes up, sometimes because the system forces the players to do it, sometimes because the players simply have access to more things that allow for increased engagement. I also find that players who also DM have a higher level of engagement.
But, yeah, for the average player that never does the DM thing, the level of world building they choose to engage in is very low.