-share, -noshare: enable/disable connection sharingThese options control whether SSH connection sharing is attempted. See section 4.17.5 for more information about SSH connection sharing. These options are equivalent to the ‘Share SSH connections if possible’ checkbox in the GUI configuration.
With -share, a PuTTY tool will check to see if there's an existing ‘upstream’ for this host. If there is, then the new session will connect via that upstream. If there isn't, the new session will become an upstream for future connections (unless -share has been given as an option to the file transfer tools, PSCP and PSFTP, which never act as upstreams).
With -noshare, this connection will not participate in connection sharing (either as an upstream or a downstream).
(This option is only meaningful with the SSH-2 protocol.)