I always hear it's important to max out your tax deferred and tax free accounts before opening a taxable account. (alephblog.com)
So not only was I able to double the position in a tax free account, I was also able to do it at a cheaper cost basis than the original position. (moredividends.com)
They put you in different ETFs if you're in a tax free account (not MUB, for instance, since there would be no point). (mrmoneymustache.com)