I completely understand because my setup is pretty much the same. I use my desktop PC for developing and doing CAM work on and then a little cheap netbook to run my CNC in the other room. As such I can't in good conscience confine users to using PixelCNC on any number of computers. Feel free to use it on as many computers as you need to.
There's no anti-piracy/copy-protection mechanisms integrated into PixelCNC to prevent users from making as many copies as they wish, or from running it on as many computers as they choose, and while this may change in the future there are currently no plans to integrate any annoying anti-piracy or license enforcement mechanisms into PixelCNC. I'm trusting the researchers who've shown that the cost of implementing anti-piracy measures is not justified by the minimal increase in sales. I can only hope that users respect my efforts and appreciate PixelCNC by its own merit enough to do the right thing.
Thank you for asking and let me know if you have any further questions/comments/concerns. :)