Basically its an ion exchange. You have you water that is pumped through a substance that will attract the phosphate due the opposite charge from my understanding. It almost works like the DI chamber of a RO/DI Unit. The best units are those that use the iron based compounds to bind the phosphate because it won't leach it back into your system once the compound is depleted.
As to the question is it beneficial, well it depends on how much phosphates you have happening in your system and what type of reef you are wanting to have. If you have a softie/zoa reef then I would say no you can probably control it with cheato and good water changes. If an SPS tank I would say yes because again from my understanding SPS corals require a more pristine water conditions.
If you have a reef system and are having an really bad algae problem I'd probably use it to get your parameters under control and then discontinue once you have found the source and eliminated the problem.
JMO - HTH