This.
No wood does well over the long haul outside unless you like weathered gray, at best, and black mold, moss, and a host of other issues in many cases. On finished wood there's the upkeep required to keep the finish from degrading, typically measured in months, not years. Covering outdoor furniture just about eliminates all those problems. The only problem I now have with the two pieces I keep covered is the wasps like to build nests up under the covers so I get an unwanted surprise sometimes when I pull the cover off. Nothing is perfect, but dealing with a few wasps is nothing compared with the nearly yearly maintenance before I started using the covers.
John