Whether a map-object should be static or dynamic can depend on a whole host of factors. Are there enough dynamic entities to support it? How about enough static entities? Might it need to be killtargeted? Does it interact with the player? Will static reduce network traffic or just overflow the signon buffer?
We don’t presume to know, so we offer the choice on all the unchanging* map-objects supported by Quoth, even the original Quake models like the torches. However, there are a variety of map-objects to look at, and different classes have different default settings.
For this reason, all map-objects keep spawnflags 1 and 2 reserved. On entities which default to dynamic, spawnflag 1 will change them to static entities. On entities which are static by default, spawnflag 2 will make them dynamic instead. The opposite spawnflags do nothing by design – this means you can select a bunch of map-objects and give them all spawnflag 1 to make them static, without having to check if they were static to begin with.
And yes, if you apply both spawnflags the entity will always be created as the opposite to default, regardless of what that was. This option is retained for contrarians.
* This is a get-out clause to exclude things like Exploding Crates or Marsh Lights that obviously need to be dynamic to operate