It solves a bunch of stuff caused by IMAP being a bit of a mess. Top of the list of JMAP benefits is:
[JMAP] is stateless. It doesn’t need a persistent connection, which is better for mobile use, which may have intermittent network access and where battery life must be conserved by turning the radio off whenever possible.
This looks like the kind of thing I would like to use, but I’m already tied into the plain markdown files “ecosystem“. Maybe I can import my stuff into anytype?