Personally I think that usually means Stay IN line of sight. Particularly when its a healer shouting at a tank! While I "generally" prefer people to type out in full I suppose it depends on the situation. If you are in a random group without vent and you type as healer, "Please dear tank, it would help me greatly if you would stay in line of sight", then the tank is probably dead before you are half done typing.
---------- Post added 2013-02-13 at 04:54 PM ----------
Or if you are in England, something you might have for dessert. It would be Jam you would put in your sandwich here (although personally I prefer ham and cheese).