Excluders are a "must" if you are running single brood chambers (Langstroth
or smaller anyway).  If you can tolerate a bit of brood in the first honey
super, early on, you don't usually *need* them for double- or triple-brood
chamber hives. The brood in the honey super eventually gets replaced with
just honey.  At least that seems to work well here.  It is good, as we
don't have to worry about the bees sulking below the excluder, &
procrastinating in getting to work in the first supers.
 
Then, too, with an early nectar flow the bees will fill the upper part of
the brood nest with honey, and the queens will not get to lay in the first
supers.  This is the situation during some springs.
 
One recommendation I can offer, fwiw:
 
Go with the metal-bound wire excluders.  The wooden-rimmed ones cause way
too much burr-combing, as they result in too large a bee space on one side
or the other.  The metal-bound ones stay much cleaner, and besides, the
wooden rims tend to rot and fall off anyway.
 
The metal ones are cheaper, as well.
 
my two cents...
 
best wishes
 
Joel Govostes              Freeville, NY