Storing in wooden crates which are usually used in the UK and cooler parts of the United States has quite a few drawbacks. 

You can't access your items very easily. More often than not the crates are placed together and high up in a warehouse. You'll need to give the warehouse plenty of notice to agree on a suitable time for both parties to gain access, and they are not that easy to stack your belongings into. Large items such as beds, sideboards, and sofas mostly won't fit inside either. You can't lock the crates so the door can be removed at any time. The wood gets very dry creating lots of dust to cover your things and varying temperatures inside the crates can distort your belongings such as wooden furniture and sentimental photos etc. 

Self-storage rooms are inherently better suited for storing your household furniture and effects. They are constructed with strong metal panels and they have a solid floor. They are taller so can accommodate the largest of sofas, beds, sideboards etc. With more room to move you can store your things more easily. They are also less of a fire risk and much more secure than effectively a wooden box! And above all else, you can get access easier and much quicker any time you want during our opening hours. You have your own code for the padlock so you have peace of mind knowing no one else can access your room. They even have closed-off ceilings! 

And due to constant steady temperatures throughout the year, your stuff will stay in better condition with zero chance of damp.