snc/accept_insecure_gui is a SAP Parameter attribute which is used to control Accept insecure SAPGUI logins to SNC-enabled Server information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
By default, after the Secure Network Communication (SNC) module has been
activated, the SAP application server rejects all conventional
(non-SNC-secured) connection requests from SAP GUIs.
If you want it to continue to be possible to log on with old SAP GUIs
and unprotected connections, you need to configure that using this
switch.
If you continue to permit conventional logons, it is left up to the
users whether they perform secure logons, and protect their data while
it is transferred.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.