Eliminating (or at least reducing) the taxes on Social Security is a big one for me (even though I stopped paying INTO SS in 1979).
This year, fully 85% of my "SS equivalent benefits" are taxable.
Had that been 0%, or had there been some kind of "limitation" (say, a maximum of 30% of benefits to be taxable in all cases), it would have reduced my taxes quite a bit.
As it this year, no refund -- I owe the IRS instead.