Portability depends on the weight and compactness of the sleeping bag. If you’ll be hiking for several days, you’ll likely be carrying your sleeping bag, food, a change of clothes, a tent, and other essentials. This means you should look for a compact sleeping bag that won’t be too heavy or cumbersome. If you’ll be returning to the same campsite every night, you can afford to bring a bag that’s a little heavier. In summary:
For hikes lasting several days, choose a lightweight, compact sleeping bag that won’t be too difficult to carry.
For overnight hikes, opt for a more comfortable sleeping bag. It can be a little heavier but should still be compact.