May not be important for some applications but can save a big headache or lots of complicated circuitry -- any 3-phase motor is oh, so easy to reverse. Some single phase motors can't be reversed and others take a lot more hassle than just reversing any two leads on a 3-phase motor.

If you have long runs and are figuring voltage drop for 1-phase loads, you need to figure the distance out and back to come up with total drop due to resistance. 3-phase just needs to be figured for the distance one way so your resistance losses will be 1/2 or slightly less because a same size motor uses less current on any leg of the phase. Note that this doesn't mean that it takes less power to run a 3-phase motor, only that the 3-phase circuit is delivering current on 3 lines and the 1-phase is only using two so they need to carry more to deliver the same number of KW.

Unless the demand charge is out of sight, I'd need a lot of convincing before I'd pass up 3-phase.