1) It will mandate that all Americans get coverage.  (I'll ignore for the moment the philosophical and ethical question of whether the government should force me to buy something from another citizen merely because I exist.)  

2) To make sure that it's affordable, Medicaid eligibility will be expanded to those earning 133% of the federal poverty line.  

Right now, Katherine and I are living below the poverty line.  We also do not have health insurance that covers us in the U.S.  (We have traveler's insurance, but when we lost our insurance at the end of February, we knew we would be leaving the country fairly soon, so we opted against buying insurance.)  When we come back to America (whenever that may be), we almost certainly will not have health insurance right away.  While far from ideal, we are more or less okay with that, and will adjust our health-care consumption accordingly -- not going to the doctor unless very ill, not changing the prescription on the glasses we both wear, etc.  Perhaps if we were sick, a family member might chip in (as a goodbye gift, we got dental exams from my parents). 

Under Baucus' bill, now it would be a crime if we chose not to enroll in health insurance, and we would definitely choose the free option, Medicaid, which would then pay for our medical care.  So my question, referred to at the top, is how a) this will decrease the overall amount of spending on medical care, and b) this will lower the government's medical expense?