It is all about capturing the ACA subsidy. When I harvest gains, I'm in at most the 22% bracket. When I harvest losses I'm in a negative bracket. Being in the 22% bracket every third year and negative otherwise beats the heck out of 15% every year!
I'm still not sure I understand the plan here, so let me see if I have this straight.
Some years you're in the 22% bracket, which tops out out $82.5k for a single filer or 165k for MFJ, and in that year you don't get any ACA subsidy or other tax breaks so you pay something ridiculous for healthcare, like $10k for one person. To offer a simplified example, you might sell $100k worth of winning stocks that generate $80k of gains, pay the LTCG rate of 15% on approximately half of that 80k, then pay $10k for insurance and have approximately $85k left over on spend on rent and food and whatever.
Then for the next few years you tax do tax loss harvesting, selling more losers than winners such that you still have income, but your net taxable income is negative. So you might sell 42k of winning stocks and 43k of losing stocks, for $85k of income that shows up as a taxable loss. You pay zero in LTCG taxes and $1k for health insurance, leaving you with $84k to spend on rent and food and whatever. You've effectively received a $9k ACA subsidy in two years, in exchange for paying an extra $6k in LTCG and full freight on health insurance in one year. Is that right?
In this situation, it looks to me like the only limit on not qualifying for the ACA subsidy every year is the amount of losers you have available to sell. Is that the problem?
Because the alternative would seem to be to just play it straight up the calendar, selling like $90k each year with a mixture winners and losers, and taking a partial (reduced) ACA subsidy each year. I suppose it depends on exactly where your income requirements sit with respect to the subsidy cliffs, huh? Just like with consolidating income tax deductions, it only makes sense for certain income bands.
This might be a little more "nuts and bolts" than the OP wanted, but if it saves me (18k-6k)=12k over a three year span, that's a nontrivial percentage of my retirement budget.