I think it depends on the scale. If your largest monthly expense is your electric bill; its not really a hobby any more.
yeah this is pretty much the case.
In the dead of winter I have done 690 usd for a power bill running 22 gpu's and 11 pc's
Kind of not a hobby at that point.
Now have I made a lot of money since 2012 no. Maybe 7k in 3 years and 3 months .
So it is a business but not too big in my case.