Under the new federal tax law there is a $10k limit on how much state tax may be deducted from your income for the purpose of calculating federal taxes, and by

Under the new federal tax law there is a $10k limit on how much state tax may be deducted from your income for the purpose of calculating federal taxes, and by opting in to this deduction you opt out of your "standard" deduction which is $12k for an individual or $24k for a married couple. Under some circumstances it may still make sense to take the up-to-$10k deduction, because it may be combined with other deductions which will add up to more than the standard deduction, but for someone paying much less than $10k in state taxes it is probably more advantageous to simply take the standard deduction, and for someone paying much more than $10k the deduction may only represent a small portion of their state taxes.