@Kuovonne says - not so fast. There are issues with custom formulas.
Airtable attracts a lot of novice script writers
So what? Google Sheets have attracted almost a billion novice script writers from its 1.85 billion user base, but it found a way to support this idea more than ten years ago. Insulating a platform from a poorly-crafted script is a process known as sandboxing. Script sanitation has been proven effective since 2007.
formula fields update with each key press
And this is good, not bad. There are currently about a hundred formulas in Airtable, and some update every 500ms. You can use Now() to get into all sorts of trouble. The platform is rife with ways for novices to make a mess. But even when users do stupid things, the Airtable platform doesn’t crash.
There is absolutely no reason that custom formulas would not exist in the Airtable platform. There are vast reasons they should exist. Airtable has feeble financial formulaic capabilities. On this dimension alone, entire aftermarket libraries would exist that could plug-and-play.
SideBar: I tried to respond to her comments where this post was originally created but it was [still] a shit-show. I reluctantly published this article there to see if it was any better, hoping no one would comment.