"Never let the customer go down the street to another store—he might find they sell the same thing there and not come back."
Mike Bloomberg in Bloomberg on Bloomberg

When people talk about cross-selling in professional services firms, there is a tendency to look only at the opportunities for growth. However, as the quote above points out, that misses the risk; if another firm starts working with your client, the client will discover just how great your competition is, and perhaps worse, what great value they are. Failing to bring colleagues into a client risks losing control of the relationship altogether. 

Where there is potential risk is bringing the wrong colleague into a matter where their skill-set is not the best possible fit for the client. This is where being able to foster both awareness and trust is so critical. If a Partner can research the experience of colleagues and develop a better understanding of their interests, they are much more likely to introduce them to clients.

Collaboration is not a zero-sum game, even if a colleague does not immediately reciprocate. Being able to address matters that are greater than any individual is how complex issues get addressed. It makes the whole dramatically larger than the sum of the parts and thus represents the rasion d'être for large firms, and the largest opportunity for growth. 

Bringing the right colleague into a conversation to address client needs simultaneously enables your professionals and firm to grow and prevents another firm from getting in the building. 

This is why having a structured way of fostering awareness and trust amongst colleagues is a continual strategic priority for so many firms.