It's obvious why the documentation says you should put the horse before the cart,
but in fact, it is possible to create both Unix and Windows services without the
geodatabase to which the service will connect. You can't, of course, connect to
the unpopulated geodatabase, but you can create a broken service (folks do
this all the time).
Back when I created services on Windows, I usually created the service first,
since it populated the ORACLE_SID in dbinit.sde (which often needed to be
changed anyway, especially back in 'sdesetup -o install' days). I've quite
literally done this hundreds of times.
So, while you certainly shouldn't bother with application servers, and if you do
set out to create an application server service, you should always enable the
enterprise geodatabase first, but if you still choose to create the service first,
then there still exists a chance that you haven't yet hopelessly misconfigured
your server (provided you immediately complete the geodatabase install).
- V