This is a minor bugfix release which is not necessary for users of Joinmarket exclusively via the command line, or JoinmarketQt (i.e. if you don't use the RPC-API). However upgrading will not hurt.
Please read the release notes at https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/docs/release-notes/release-notes-0.9.8.md for details on what this release includes.
(No Windows Qt binary is provided, as per above).
The release also includes OTS timestamp files of the gpg signatures provided, that can be verified using the opentimestamps client.