I track pretty carefully because I'm taking advantage of the ACA's subsidy and the silver level cost sharing, and staying under a certain dollar amount is VERY important in order to keep from owing, and for the purposes of making sure I can get the cost sharing perk the following year.
But if we weren't interested in the insurance angle, I'd probably be much less involved in budgeting/tracking expenses.
But you just need to plan income for that, not expenses.
In my case, I am having to take RMDs on some accounts, and we also take out more throughout the year (dividends and cap gains usually) from our portfolio to support the spending (at least during the good times the money comes from the portfolio). I have to be aware of what money is in play during the year from dividends/cap gains and RMDs, and how much I'll need to generate out of the portfolio if they don't cover all our yearly expenses.
We're not perfect at staying on budget, so for us it does require keeping an eye on a monthly budget and then making sure we stick to it as best we can so we don't end up having to pull out more from our portfolio, thus bumping us up over our projected income as reported for the ACA. It wouldn't take much to knock us up into a higher bracket as far as the subsidies and to a lesser extent, cost sharing go. Since there is no claw back on cost sharing it may not be as much of a concern as the subsidy limits, but we have no idea if they block you from estimating your income low enough to continue to receive the cost sharing benefits if you have consistently blown past the estimates each year.
We're also in the early part of FIRE, so I feel like it is still a smart move to track our spending for a while to see where we are strong and weak on budgeting/spending and work out the patterns.