When packing your storage unit, the more organised you are the more you will be able to pack in and the less likely you will be of incurring damage. This is where having a shelf in your storage unit comes in.
When choosing a shelf:
Avoid Damage Put all your fragile items such as lamp shades or paintings on the top shelf. No risk of damage here when you are moving things around the unit.
Save Your Back If you have very heavy boxes, you can place them on the middle shelf, at carrying height, therefore avoiding the need for bending to pick them up. Also, no risk of crushing other boxes by stacking them on top of other boxes.
Maximise Space Non stackable items such as sofas, barbecues, etc, take a lot of room as nothing can be placed on top of them. However, by placing a shelf over them, you will create more storage space. This means renting a smaller storage unit and saving money!
Find Things Easily No need to rummage through your storage unit looking for that specific box / item. A shelf will allow you to be more organised. At a glance you will be able to see where things are.
Avoid Breakages By not stacking boxes on top of each other and giving them a dedicated shelf instead, boxes are less likely to collapse. If a box has collapsed, when you pick it up its content may drop out of the box onto the floor and break.