To be honest, the only benefit *I* see of getting a fourth memory channel is that it grants you an extra two slots for DIMMs, meaning you could cram in more RAM. For a gamer, this is pointless; 2 modules is all you'll actually need to make use of; a pair of inexpensive 4GB DIMMs is all but overkill for any game in Windows 7.
Now, for someone doing obscene levels of audio and video editing, one could quite conceivably want an SSD's amount of RAM. For instance, someone composing music might be using a very exhaustive set of uncompressed samples, and some of these libraries ARE measured in the tens of gigabytes. So in this case, the option to go to 64GB (8x8GB) or to be able to AFFORD 32GB (as 4GB DIMMs are a fraction the price of 8GB DIMMs) could be a godsend to such professionals. The further memory bandwidth isn't of any real use; it's just the extra capacity that gets used.