It depends on your individual situation and what savings vehicles you have available to you. If you have a high salary and a traditional 401K at your employer (which was our situation), then your options are limited.
You can fully fund your 401K, but you can't make a deductible contribution to an IRA so you can't get any more pre-tax savings. You can't contribute directly to a Roth because your income is too high. So the only things you can do with after-tax savings are put it in a regular taxable account, make a non-deductible tIRA contribution or do a back-door Roth conversion. You're better off doing the back door conversion with as much as you can because at least it will grow tax free from there.
In DH's case, we did the back door conversion once that strategy became available. His entire tIRA was after-tax savings, so we converted it all, paid tax on the gains to date and added $6500 every year while working.
In my case, I had previously rolled over 401Ks from several jobs into my tIRA, meaning most of it had never been taxed, so conversion was impractical and the back door conversion strategy was unavailable to me. I just continued to make non-deductible contributions to my tIRA. I'm doing some conversions now that we're in ER and have low tax rates.