The "windowed" seat provide multiple paths for the fuel to enter the bowl.
As mentioned, it allows the bowl to drain back to a lower level, if drain back is happening in the first place.
Leaving off the little clip on the needle prevents drainback from happening at all.
The only downside to leaving off the little clip, is that it is possible for the needle to get stuck in the seat if the fuel goes bad. I NEVER see this with the fuel we have available to us currently, it doesn't stick around long right to start with, and doesn't seem to have the additives to promote the formation of "varnish" or anything else in the bottom of the carburetor when it dries up.....Cliff
