[colin25]

ok..seems it does this

It gives you the option of using a 5Ghz connection with suitable devices whilst also using the usual 2.4ghz wifi connection at the same time.
5Ghz will give faster speeds at short ranges (same room) but doesn't have as good a range as 2.4Ghz. Having the option of using 5Ghz is also better for use in congested wifi environments as less neighbours are likely to also use it (for now at least).. so less interference from other devices/wifi networks.