RPI's online communities (most notably: its subreddit, /r/rpi, but also including yikyak) suffer from high amounts of toxicity. This is a concern of those in charge of moderating the communities, and an effort has been made to help cut down on some of these problems (i.e. sockpuppet accounts, brigading, trolling, completely anonymous harassment).
There are a few core parts to the linking system. It allows for account creation using a sign-in through a supported service (at this time: discord, reddit, and RPI's CAS). Once this has been done, users can link remaining services to their account on the site.