I use an Excel model for basic financial planning. It tracks and projects spending, investments, taxes, and the withdrawal plan. I also use it for periodic what-if's and decision-making, especially WRT taxes. Mostly, I use it for ongoing stuff like tracking monthly spend and quarterly tax estimates.
Periodically, I update assumptions and run the long-range projections. I then check it against FIRECalc, RIP, and/or i-ORP. I only do this once or twice per year now, usually in conjunction with some big change (like eliminating file/suspend), or prior to the annual visit with our Fidelity Private Client Group rep. In the years just prior to ER and for about a year after, I ran these models monthly and sometimes weekly. Just anxiety about the big paycheck ending and the fear that I missed something.
For many early retirees, I think it's still important to run these analyses at least once per year, primarily to ensure that the burn rate is still sustainable under current market conditions. I think if you are further along in retirement with SS, and maybe a COLA'd pension and LTC insurance, then there's probably little benefit.
For us, we're still spending about 30-35% below the level recommended by FIRECalc/i-ORP, and we cover a large percentage of spending with pensions and rental income. So the money-related anxiety has gone down considerably last couple years. As long as our spend is under control and the market behaves itself, I don't sweat the details as much as when the paycheck initially stopped.
OTOH, if I was 48 with kids in college and totally dependent on portfolio withdrawals, with high health insurance costs and a big mortgage, I'd probably be checking FIRECalc a lot more frequently.