When you start looking into storage options, you will soon find that you have two main choices: non-climate-controlled or climate-controlled storage. In most cases, unless you're storing only outdoor equipment, you will want to rent a climate-controlled unit. That is because climate control helps prevent a wide range of issues, including the following.
Where there is heat and moisture, there are often insects. You might figure insects are not a major issue if you are not storing food for them to eat, but some species of cockroaches, and even ants, are happy to eat items made from paper, glue, and even wood in some cases. Choosing a climate-controlled unit is a good way to keep insects at bay since they need moisture to thrive and climate-controlled units won't get nearly as humid.
If you have mold growth on something like a sweater or sofa, that item will basically be unusable when you remove it from storage. And even though you could remove mold from a hard item like a fridge or oven, you really don't want to have to! In a climate-controlled unit where the air is less moist and temperatures are kept manageable, you should have far fewer issues with mold growth, meaning you'll actually be able to use and enjoy your items again.
Exposure to moisture is terrible to anything made from wood, particleboard, or any other porous material. The moisture can cause picture frames to bend and distort, furniture legs to bow, table tops to warp, and more. Once an item distorts, getting it back into its original shape can be really difficult and expensive, and it's not often worth the effort. Save yourself the headache by choosing climate control, where the consistent moisture level will keep everything as safe as it would be in your own home.
Electronics are pretty sensitive to high and low temperatures. This is especially true of computers and anything else with a "chip," which most appliances will have as well these days. You would not want to put your microwave or computer into storage and pull it out, only to find it won't turn on. Climate control protects electronics.
Look into climate-controlled storage units in your area. Although you will typically pay a bit more for a unit of this type, it is well worth the cost when you consider how many issues it will prevent.