[hoffspot]

You hit on my first thought. There are numerous legitimate user experience cases where keystroke by keystroke or field by field processing is beneficial. Autocomplete for address data is one I see commonly used. Saving a partially filled out form field by field in the event a user becomes disconnected and would like to complete it later is another. From a security perspective, I know of numerous tools that examine the speed and cadence of the act of typing to discern between bot entry in a field versus human entry. There is also software like FullStory that records everything client side, including mouse movement, so companies can determine exactly how people are interacting with their sites in an effort to improve the UX. And from a tinfoil hat perspective, if a user is interacting with a webpage, they should assume everything they are doing on that page is subject to observation by the page author. If the researchers were surprised by this, I fear it's from inexperience.

[zzo38computer]

Even if it is beneficial, the user might still want to disable it. (Possibly a option in the browser for manual/auto calculate; if manual, then events are disabled until you push submit or recalculate. This might improve speed, too. Another thing that might be useful may be ARIA mode (which can also have other advantages, although other things are needed too anyways).)

Saving a partially filled form is something that should be a feature in the browser, you can do "File > Save Form Data" (and then specify the file name) and "File > Recall Form Data".

I generally disable JavaScripts. Sometimes the web page will still be displayed if CSS is also disabled (and sometimes I want to disable CSS anyways), and sometimes links to original data, etc can be found if you view the source.