>>How does that differ from a sale ( in it's effect? )

In usual inventory parlance, a transfer is paired- an issue from one location paired with a receipt to another location for the same quantity. If the cost is being maintained at the item/location level, the receipt to the new location will start a new FIFO stack.

A sale, or any issue that is not paired with a receipt (dumping obsolete parts for example) will not be paired. From a FIFO point of view, they are identical- they decrement the stack- but there usually are other statistics being maintained that will be treated differently for a sale and an issue.