Won't add much than what you said apart from the reconnection feature !
According to this and this as you said :
p2p.Server should be able to use a JSON file containing trusted node
addresses. It should try to keep those nodes connected at all times.
The connections should not count toward the maximum number of
Trusted nodes are privileged: they get connected/accepted even above
the maximum peer count Connections to trusted nodes are reattempted
every once in a while (15 sec for now)
In geth code you can see the comment:
// Trusted nodes are used as pre-configured connections which are always
// allowed to connect, even above the peer limit.