The adjusted gross income number (AGI) is an important one. It is said it is always better for a deduction to be for AGI, i., deductible...

The adjusted gross income number (AGI) is an important one. It is said it is always better for a deduction to be "for" AGI, i.e., deductible in arriving at AGI. These are also called "above the line" deductions. Why is it better? Can you name any specific benefits to being deductible above the AGI line?  Discuss one or two "above the line" expenses or adjustments to income from the front page of the 1040. Why policy reason do you think made these above the line deductions instead of as itemized deductions?