I don't give a single thought to how much was principle and how much is growth. Moot point anyway for me to even consider since at this point I doubt I could come up with things I want to spend money on that would even eat into the principle enough to matter. (I am not a big spender). I am not interested in leaving any legacy and if there is money left over, it's going to charity anyway.
I have an inherited IRA, lots of IRAs (one each of a Roth and traditional/rollover) between myself and the spouse and a taxable account with my brokerage (all accounts are with the same company - Fidelity).
I linked up my checking account (brick and mortar) with my taxable investment account.
When I have to take a distribution (required minimum distributions are necessary each year from an inherited IRA if the person you inherited from would have been taking them if they were still alive), I have them sell off equal parts of the 3 funds I hold in that IRA, then take out federal taxes at 10% (and send that part off to the IRS) and the remaining cash is transferred to my taxable account. From there, I can decide to reinvest that money in my taxable, or set up a transfer from my taxable to my checking account for spending.
I have an automatic plan in place for the first part (sell funds, pay tax, transfer to taxable account on X date). I can go in and modify that plan at any time and have - change the date, increase/decrease federal tax, change it to take the amount from only one fund, etc... Or I could just do it myself without an auto plan, or I could call up my rep and ask them to do it (but don't see the point to that at all).
Takes about 3 days total for the money to move over to my checking account as of now, but my understanding is that the ACH debit/credit transfers may be getting faster in the coming year for some institutions. In any case, the ACH transfers are free so I don't mind waiting a few days for the moves to happen. And bonus - they count as "direct deposit" so my checking account with the fussy bank I use doesn't get to charge me a service fee since that is one of their requirements for a free checking accounts. ;)