If coils are not properly maintained and left unobstructed, your system will have to use more energy than it should to function properly.
This could eventually lead to your system overworking itself and breaking down.

The AC coils and fins on your outside unit can be cleaned rather easily with a standard broom and a garden hose. You can also use a nylon brush if you prefer. Wash the parts to get any obstructing elements off of them, such as leaves or other debris.

While you may think that using a pressure washer will do a better job of cleaning the parts, you should never use one, as its strong spray could actually cause more harm than good.

If you have an inside AC unit, you can clean it in a similar manner prior to installing it for the hot months and before storing it away for the cold months.