I originally hid my dock on the left, but now it resides hidden on the rhs. (I can't quite recall, but I think some apps would not open flush to the lhs and it bugged me.)
Perhaps this poll should also ask about location and icon size too, to make it more comprehensive.
[EDIT] It was also because I could not access the portion of the window underneath the dock if I had it exposed on the rhs ... hence my move to the lhs. After a while I decided to hide it.