Nope, it doesn't hurt a thing. If your toilet uses raw water, disconnect the head intake line from the thru-hull (it's prob'ly a good idea to close the seacock first), stick it in a jug of antifreeze...flush the whole jug through the toilet. Do not reconnect the intake line to the thru-hull. If more antifreeze is needed in the tank, pour it down the toilet. If you have an overboard discharge pump, turn the y-valve and VERY BRIEFLY run the pump to pull antifreeze through it and that plumbing.
If your toilet uses onboard pressurized flush water, winterizing the fresh water system also winterizes the toilet. Remove any water in the bowl. Put any antifreeze needed in the tank into it through the toilet.
After the boat comes out of the water (if it does), open all seacocks to let any water in the lines drain out. Make sure your bilge is dry.
Btw...if you're thinking of using vodka in the fresh water system as an alternative to the "pink stuff," vodka only works if the temperature stays above freezing. Before someone squeals...UNCUT vodka won't freeze to at least -10...but even a 90-10 cut with water will freeze above -0- So unless you vacuum ALL the water out of the tank, you'd need more than 10 gallons of vodka for every gallon of water left in it...and if you DO vac all the water out, you don't need antifreeze OR vodka, 'cuz it's ice that does freeze damage, not cold temps...and if no water is left in the tank to freeze, there can't be any ice.