The number of currently unused bytes in the cache.
When the cache is empty, this value equals maximumAvailableDiskSpace. As AssetBundles are stored in the cache, this value will decrease. Caching manages cached content based on a Least Recently Used (LRU) algorithm. If insufficient space is available in the cache to store a requested AssetBundle, the oldest AssetBundles in the cache will be iteratively removed until enough space is free for the new AssetBundle. This property does not account for total available disk space. If a user's computer has less available disk space on the drive where the cache is located than spaceFree, the full amount of spaceFree will not be usable.