rrands, welcome to the forum!! The valve you have only allows you to filter or backwash, the multiport provides more functions (at least one of which you need -RINSE- to prevent the sand os Zeo from entering the pool after backwashing). In addition to filter and backwash, the multiport has settings that let you:
1) recirculate the water - ie keep the water flowing through the system without entering the filter (this can be handy if you develop a filter problem, you can have the filter fixed while still circulating the water and chems)
2) lower the pool water by 'wasting' it out the backwash hose without having to backwash.
3) close the valve so as not to lose prime or send 'crud' back into the pool while opening the filter
4) rinse the stuff out of the tank that was liberated by the backwash process to the backwash/ waste line - this is what thepoolman was talking about, the stuff (be it dirt, algae or Zeo) that didn't exit the tank is still in suspension in the top of the tank after backwashing, so it gust gets pushed through the returns if you don't 'rinse' after backwashing & doing a couple of 'bacwash/ rinse' cycles cleans the filter better.
Hope I've explained things ~ clearly, if you need more info please ask, (thepoolman may have other reasons why the multiport is 'better') and the nice and knowledgable folks here will give you their insight.
Again, welcome! - Waste