-share: Test and try to share an existing connection.This option tries to detect if an existing connection can be shared (See section 4.17.5 for more information about SSH connection sharing.) and reuses that connection.
A Plink invocation of the form:
plink -share <session>
will test whether there is currently a viable ‘upstream’ for the session in question, which can be specified using any syntax you'd normally use with Plink to make an actual connection (a host/port number, a bare saved session name, -load, etc). If no ‘upstream’ viable session is found and -share is specified, this connection will be become the ‘upstream’ connection for subsequent connection sharing tries.
(This option is only meaningful with the SSH-2 protocol.)