You make one link and PI3 does the second automatically for you. In other words, you insert Christine Dey in the associates list of Bert Wooster and, automatically, Bert Wooster will appear in the associates list of Christine Dey.

Incidentally, if your contacts are actually businesses, you can use this facility to provide a list of companies that are associated in some way. Great for when you are trying to trace a web of 'shadow' companies.