8 Vs 4 ohms

I have a Rogue (tube 55W) integrated amp that has 4 & 8 ohm taps. I have Dali Helicon speakers rated at 4 ohms and curretnly I am running them on the 8 ohm output from the Rogue. Does this hurt anything, what differences in sound could I expect running 4 Vs 8>

Thanks,

dan