Here goes:
After frames and hive bodies have been in use for more than a year or two,
there is always a buildup of propolis and wax on the frames, the insides of
the box, and on the rabbets that support the frames.  Many beekeepers find
that it makes things much easier if you remove one of the 10 frames and
spread the remaining 9 out a bit.
 
Benefits:
-Easier to remove each comb, often without having to pry the stuck frames
apart.  (This means it's less likely you'll bust a frame end bar.)
-Certainly easier to remove the first frame to make more room for
manipulations.
-Increased ventilation and clustering room in the brood nest. This has been
said to relieve congestion considerably (acc. to Walter Kelley, Chas.
Dadant, R. Taylor, others)
-10% reduction in brood-frame-costs per hive.
 
Disadvantages:
-The combs are best constructed (initially) with the 10 frames together, so
that                                                 they are built evenly.
-Attention must be given to manner of spacing, if this is to work well. The
end-bars are spaced so there's about 1/8" between them, this results in 1.5
inch (on center) comb spacing, approximately.  This is acceptable by bees
of European descent in the brood nest.  There is then about 1/2" space left
over at each side wall. The bees will draw the end combs out a bit deeper
but they are still easily removed.
-Frame-sway.  This may be a problem with clean, new frames, or when the
bees haven't had time to stick things together.  After a couple of days,
however, the frames are usually cemented in place by propolis and aren't
apt to move.  Also, once a colony is fully occupying a brood-box they brace
the fixtures well. Propolis deposits on the end bars then act as solid
spacers, and the frames can be pushed together with the correct spacing
automatically maintained.
 
NO, there isn't enough space for a good queen's brood on 9 frames.  Yes,
the outside combs hardly ever are used for brood.  But then the usual
practice is to use 2 brood boxes anyway. So the queen still has more than
enough room.  You can also use these conditions to your advantage:
 
By keeping the best quality combs toward the center of the brood boxes, you
ensure that the queen uses them for laying.  Poorer or incomplete combs can
act as the "outside" combs, next to the wall, where they are not wasted,
but filled with food stores.  Comb quality there is not so important.
 
and...WINTERING:  With two or more brood boxes there is plenty of room for
winter stores.  PLUS there is the added advantage of more cluster space
between the combs.  This allows better continuity to the cluster and, I
suspect, better wintering success. Not just from 9-frame spacing, however.
I find that the bees do better when they are provided with a good space
under the lid where they can cluster across the frame tops.  You can
provide this by flipping the inner cover over, or with an added 1-2" rim.
This also provides a place for administering dry sugar or candy in late
winter.  I hope this explanation is helpful -- JG