This is a vanity feature. You can flaunt your friends with this.
Expose is one of those. It specifies whether you'd like a person, place or group to appear listed in your profile. This is equivalent to a top friends type of listing in typical social network applications.
You can specify the degree of exposure of a UNI using the /expose command. 0 is to never show and 9 is to show always. In between values make it more or less likely depending on the degree of trust you have for the person who is requesting the profile from you.
The /show expose command tells you who your top friends are. /set friendsexpose and /set groupsexpose set the default degrees of exposure.
The /cancel command lets you delete the entire record for a peer.
P.S. psyced currently doesn't implement exposure maths correctly.