If you re-buy the same things 30 seconds after selling, that is a "wash sale". Please look up the wash sale rules. The bottom line is that if you sell (at a loss) and re-buy the "substantially identical" positions within 30 days, you can't deduct your loss. Rather, the loss gets added to the cost basis of your new position (and you can deduct that loss when you eventually sell the new position).

Now, let's pretend that you're not buying "substantially identical" positions, but are instead buying something that gives you exposure to the same thing (e.g. you're selling one crypto index fund and buying another crypto index fund). You are going to be able to deduct $3000 on your taxes this year and have $12000 to offset potential gains next year. To me, that doesn't at all feel like it would be worth $800 in fees.

The $800 in fees are probably going to basically equal what you're saving in taxes by getting to deduct the $3000. So it's not like you're walking away with any extra cash today. I just can't see that being worthwhile.

(And again, if you sell stuff at a loss and buy that identical position back, then you can't deduct it anyway.)