The hacksaw takes an hour and a half to get through a tree limb when an axe takes 45 minutes.
This is why it's always a risky option in long term survival - you can keep repairing it indefinitely as long as you have metal (unlike the axe and knife which will eventually run out of whetstones to sharpen). And it's relatively light. But the chance of the weather changing for the worst while you saw away at treelimbs or carcasses is quite high.