Balancing Mains Electrical Loads
Given that line voltage regulation is designed to be 5% p.u. for all of distribution, it improves the voltage regulation for loads to be balanced. This also balances thermal rise in 3 phase cores and reduces aging from elevate temperatures due to unbalanced loads.  Surge currents cause further disruption of neutral shift from 10x surge currents of loads are not balanced in industrial loads that may cause over voltage on under loaded phases using single phase voltage during surges on the other two phases during startup. This may trip the breaker but can easily also damage large power supplies .

For the consumer, unbalanced loads or operating breakers near the limit may cause more rapid aging and premature failure. Otherwise a Watt used is a Watt charged regardless of which line of a split phase power meter it comes from.