Draft in US will probably slightly reign in its tendency to throw armies around in one war after another on a whim. I think that is the outcome people tossing around the idea are hoping for.
The only thing a draft in the US will do is to get a lot of people really, really angry and cause the politicians who support it to lose their offices (despite everything and all the PACS, if you have something 80% of Americans support, it will be done). If Obama does it, I would not be surprised if Texas, possibly with some of its neighboring states, leaves the union.
But yeah, it would end the system that the US has today. You can't have permanent bases overseas staffed with men drafted from their homes.
Given the military history of the US, I think that is wishful thinking. It didn't stop Vietnam or Korea from happening. Since better connected men and all women are exempt, it was unfair.
Nobody is seriously discussing a military draft in the US. Nobody actually wants it -- certainly not the generals, who already have all the volunteers they need and have no interest in babysitting a bunch of shiftless eighteen-year-olds who'd rather be anywhere else. Modern military forces require lots of expensive hardware controlled by a small number of well-trained people; we don't do cannon fodder any more.
A non-military draft to force eighteen-year-olds to go out and plant trees or pick up litter is one of those stupid ideas that gets floated around from time to time by people complaining about kids these days, but apart from being vastly politically unpopular it's almost certainly unconstitutional; the Supreme Court upheld conscription in 1918 under Congress's power to declare war and raise armies, but conscripting people for non-military purposes couldn't possibly have the same legal justification so it would have to be against the thirteenth amendment "Neither slavery nor involuntary servitude... shall exist"
But yeah, it would end the system that the US has today. You can't have permanent bases overseas staffed with men drafted from their homes.