Cashing out big gains and taxes

Not that I have this problem (yet), but wondering for US peeps, what do you do in the situation where you've had really big gains like into six figures a year.

Do you take lump sum and cut a fat check to the IRS right away, or do you withdrawal just enough to keep you below the largest tax bracket?

Also, if you leave USD on the coin exchanges such as GDAX at the end of the year because you're planning to reinvest, does that count as profit (assuming you gained)? What if you reinvest it all…

Cashing out big gains and taxes