That’s an interesting question and it’s the first time it has been asked on this site!
Based on various studies, the difference to heat air at 50 % or 30 % relative humidity is negligible, even minuscule. So, in fact, there is no difference.
We do, however, recommend you maintain the relative humidity in your home between 30 %and 50 %. The colder the outdoor temperature, the closer the relative humidity level should be to 30 %.