When you right click a mob_spawner with the NBT tag SpawnData consumes one spawn_egg if you are in survival mode and adds 1 to stat.useItem.minecraft.spawn_egg (regardless of gamemode) but doesn't affect the spawner in any way.
Comments 5
It also works in Survival and it is not "Works as Intended" because it literally changes nothing when the SpawnData tag is set. However when it is not set, it will simply overwrite the EntityId value.
this is a creative only feature