When I was a kid we raised chickens for a long time and they were pretty small. I remember getting a new variety that were huge in comparison (they finished around 8lb sometimes!) and they ended up looking great but being incredibly disappointing to eat. They tasted a lot like store-bought chicken. Big chickens are definitely less interesting on the plate in my experience.
As I recall my dad picked them because the feed to meat ratio was crazy. The chickens ended up like 2-3lb heavier on average (maybe 1/3 increase) but finished way faster and ate about the same amount. It was a no-brainer for cutting costs, and we were really poor.
Popular commercial duck breeds are similar. They're easier to turn into things you like eating I suppose, like smoked breast or confit, but flavours and textures are far less enticing and lack character. If you have the opportunity to raise your own, seek out older and more interesting breeds – there's a whole other world to explore that you'll never see in a grocery store.