It all depends on what media I'm using and where I'm planting it.

If I tie it to a tree trunk, I will bury some into the spaghnum moss, and leave other roots dangling.

Same thing if I were to re-pot it in straight spaghnum moss, for when I'm trying to revive a dying orchid.

Most of the time, I bury the roots in the medium but leave some roots just above level. I found that orchids like to have some of their roots exposed to air so I try to do my best and leave a couple of roots exposed.