There are many benefits in selecting Climate controlled storage over basic storage. Temperatures are kept between 55°F and 80°F. The units are inside an enclosed hallway away from pests, humidity etc.
When storing long-term, you'll want to consider climate because exposure to heat, cold and the elements can cause yellowing/degradation of fabric, clothing and leather items. Metal can also start rusting when it's left in the elements. Climate controlled storage prevents humidity/condensation damage that can happen in a typical outdoor "garage" type (Basic) storage unit.
If your valuables do get damage from the outside elements from a basic storage unit, the cost to replace would cost more than a climate controlled unit. Think of it as insurance for your valuables.