How do you know if a bad is open, unless you listen? With an SDR, you might be monitoring 15 thru 6M in the background. Or gathering propagation data using WSPR or FT8 decodes. It's not like you're listening to 8 nets on 8 bands simultaneously. Working 6M an up contest this becomes useful, especially if your in an area where there isn't lots of activity! Lots of folks have a radio sitting on a "dead" band, like 6M. This is no different, but instead of having multiple radios, I can use one and can monitor 10M & 6M, my local VHF repeater, while working on 20M, just as an example. There are other possibility as well - diversity receive with multiple antennas, for one. If you're using a beam on a band, having another receiver on the same band on a vertical might be useful, or vertical and horizontal antennas. For some stations with real antenna farms, why switch between antennas pointed in different directions to a single receiver, when you can switch between real-time receivers receiving ALL of them simultaneously? It can be a game changer... but nobody is forcing you to use 8 receivers either.