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BTW, FastE full duplex is optional. Although most devices, especially today, that support FastE will support full duplex. Also BTW, FastE hubs (which you're unlikely to see much of) have additional restrictions beyond what Ethernet hubs had.
If full duplex is provided, you often get some benefit even when the bulk of your traffic is flowing in just one direction. This because, often there is some back flow (e.g. ACK packets). With half duplex, you can collide against those. Full duplex doesn't have this problem. And, as Rolf noted, you do have the bandwidth bidirectional. However, although the bandwidth is practical, moving from half duplex to full duplex won't double your transmission rate transferring a file from one host to another. So, marketing likes to mention it. (Note: They don't push this nearly as much as when full duplex was "new".)
Lastly, and on the subject of transferring something like a file between hosts, remember your payload rate won't see the wire rate due to L2 and L3 overhead. Reason I mention this, people often wonder why their transmission rate is often lower, possibly much lower, then the nominal wire bandwidth. For example, a minimum sized Ethernet packet, 46 bytes, will use 84 (or more) bytes of the wire's bandwidth. Then there's also higher protocol overheads too.
