@drehb is correct
But also if the storage space is not directly attached or on your local network, then its self defeating because the time required to get the chunk from an external network would mean you cannot be fast enough to ever beat another vault in serving up that chunk.
You see there are 8 or more copies of any particular chunk and they are spread across different vaults. Then to be a “successful” GET (retrieval of a chunk) you have to be the fastest to serve up that chunk.
So if your storage is not on your machine or local storage then by the time your computer gets the chunk off that remote storage someone else will have already served up the chunk.
NOW if you rent datacentre machine to farm then the storage is local to the machine running the software so its good and they have fast everything.