Why can't I add a LAN computer to "Computers & Contacts"?

I go to "Add remote computer" and enter the LAN IP address in the "TeamViewer ID" field like I can do with "Partner ID" in the "Remote Control" tab.

But it refuses and tells me to check my input and enter a teamviewer ID. 

The only half-solution I've found is to make a shortcut as outlined in this solution: https://community.teamviewer.com/t5/TeamViewer-12/Shortcut-to-connection/m-p/1209/highlight/true#M38

I am not very happy about having passwords in plain text for anyone to read.

I mean, you got to be kidding me! Is the only way to be more productive to be less secure??