that was my thought, My house was built in 2000 and has no ice guard or drip edge, not a single icicle or damn. I just finished the building two months ago and a tree fell across it so it needs to be repaired and would be feasible to do at this time...No one had this until just recently. Now it is a must have. If there is proper ventilation and insulation in a pole barn you should be ok. I would get a roof rake to keep the snow buildup off the lower few feet.
You can still pull the lower runs off and put the ice guard on. When we did our roof we put it on the entire house and all buildings. Not that much more money. Plus I keep the roof raked.
No one had this until just recently. Now it is a must have.