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keep fiat for necessary operations
or
convert all fiat into sats
The accounting anyway has to happen so it makes not too much of a difference there, but I try to not be hyperactive about exchanging all the time because the action itself is a chore. So I think that the precise answer to your question is: when I get paid in fiat instead of sats, I never exchange everything into sats; simply because then I'd just be converting back days to weeks later and that makes no sense. So say I'd get hypothetically paid today for the coming 6 months worth of fiat expenses, in fiat, then I will at least keep 2 months worth in fiat. If I get paid today in sats for 6 months, then at the end of the month I try to make sure I can cover the next 2 months of fiat expenses too, and exchange back accordingly.
I generally find it much more valuable to spend time finding reliable services that accept sats to decrease structural dependence on fiat, than to micromanage the day-to-day fiat exposure. I guess we can call that low time preference cashflow management.
The main scenario
You went into a lot of detail and I appreciate you being so open, so I have a few more questions to dig deeper. Do you keep fiat for necessary operations and record them at fair value in sats in that complicated spreadsheet of yours, or do you convert all fiat into sats to avoid having to deal with that accounting and keep your flow "pure"?
Dealing with clients who I assume aren't bitcoiners makes the contract itself feel like an investment to them; it's very complicated, and I'll keep that tip in mind in case I have to deal with it.