No IRA’s?

35m, $350k in 401(k). Everyone seems to have an IRA in addition to their 401(k) but aside from potentially lower cost funds and investment flexibility, is it really necessary?

I max out (or try to max out) my 401(k) every year, and have low cost options (two fund portfolio exp ratio avg =3bps).

Is opening an IRA/ROTH IRA in addition to the aggressive savings into my 401(k) necessary if I feel like I’ll have enough saved in the 401(k) in 30 years? If so, why?