When you own multiple IRAs and take an IRA distribution, the IRS treats all your non-Roth IRAs as one. This helps you when you reach age 70 ½ and must begin taking annual required minimum distributions (RMDs).
Let's say you wish to contribute to an IRA in 2018 but have too much income to make a either a deductible contribution to a traditional IRA or a contribution to a Roth IRA. You still have the option to make a nondeductible contribution to a traditional IRA. Might this make sense for you?
One of the greatest benefits of an IRA is its ability to provide tax-favored wealth for heirs. An IRA left to a beneficiary can be "stretched" to provide pre-tax compound investment returns for the rest of the beneficiary's life -- or even longer. And these can be distributed totally tax free if it is a Roth IRA.