How would removing the 8th Army from South Korea help America?

"How would removing the 8th Army from South Korea help America?"

First, it might free up a large number of professional soldiers to
meet American obligations in many parts of the world.

Second, as N. Korea is recklessly experimenting with nuclear devices
and firing missiles, a large land force would be ineffective and might
be a target to an unstable ruler. On the other hand, withdrawal of
some troops might provide reassurance to a very paranoid dictator in
the north.

To continue, however:
It could signal US disinterest in defending S. Korea, creating a
defence vacuum that invited serious threats from N. to S.  In any
event, it would upset the balance of forces in the area, perhaps
letting mainland China think it could esculate its aggression against
Taiwan.
I don't think any of these eventualities would "help" America, in the
area or around the world.

To continue, however.

The US has indicated that China has a free-hand to overthrow the N.
Korean regime, but not at the cost of Taiwan (we might have to nuke
the 3 Gorges dam if it gets there, for God's sake).

S. Korea can whip N. Korea quickly, but only at great cost. Kim and
his henchmen would nuke S. Korea if only out of spite, but S. Korea
would still win, and the world would be prissy about it, and let all
the Koreans starve. It may go there, actually, and it'll be little
Kim's Iron Chef that gives us the details.

China is actually a paper dragon. Their policy of one-child-only has
resulted in one college student with two sets of grandparents who had
an only child. Fat little emperors, yes, but also educated
grandparents bearing down on a smart, educable grandchild. The
coming-into-power-generation does not want to upset the family cart.
Just as in the USA, it's all about Social Security.

China has discovered the benefits of entrepreneurial free(r) markets.
The rise in the standard of living and modernization in China make it
difficult for the ruling elite to jeopordize hard earned credibility.
To engage in a war with Taiwan or on the Korean peninsula would become
complicated and provide little or no benefit for China.

In adddition, Asia may soon be dealing with a potential pandemic from
the avian flu. If the virus continues to mutate it can jump to the
human population. Should that occur, Asia will be in a severe health
crisis. Nothing spreads disease like war. The 1918 flu epidemic killed
between 20 to 40 million people in less than one year, globally.
Today, a pandemic of flu would fly around the world in 24 hours.

Removing the troops would be a signal to both North and South
- it would probably not be a good idea

My view is that N and S Korea are conducting a complicated and
stylized wedding negotiation.

N can see that S is pretty affluent (especially by Asian standards),
but the nomenclatura are afraid of losing their privilleges. Hence
they are upping the ante by this slightly ridiculous nuclear posturing
- ridiculous because if they used it they would become a universal
weopons testing zone.

Personally I would be inclined to smother the North with kindness,
re-instate the cheap(er) oil supplies, the termination of which caused
this problem, introduce a demilitarized zone for the production of
agricultural equipment

... and perhaps most importantly, show them the benefits of Swiss bank accounts.

@Waukon
I'm not sure that the PRC really wants to overthrow Taiwan
- only recently they opened up direct flights
- and for a very long time 'Taiwan' goods really came from the PRC
- Taiwanese businessmen spend a lot of time in the PRC

I suspect that the PRC and Taiwan find it rather useful playing two
hands of poker in the same game.