The point is not that the roth ira is a useful savings vehicle for one's emergency fund, but that it's a good idea to think of the extra FAANG / MAGAM (whatever the acronym is now) money one gets on top of a non-MAGAM developer job should basically be treated as if it doesn't exist, and therefore socked away in the extremely useful retirement savings vehicle of the mega backdoor Roth IRA (which I know at least Microsoft offers). This treatment of the "MAGAM bonus" as such allows one to be able to downsize to a less-well-compensated dev job if one has to (e.g. layoffs, then go work for some non-software-first company like in automotive, consumer products, etc).

Most developer salaries put them well above the IRA limits, so having the option to save post-tax dollars in a Roth (which also has no RMDs, unlikely regular 401ks and IRAs) is a rare opportunity.